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Query: UMLS:C0026936 (Mycoplasma)
 14,761 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The staphylococcal transposon Tn4001 was introduced into Mycoplasma pulmonis using an Escherichia coli-derived vector by polyethylene glycol-mediated transformation. Using a reaction mixture containing 10 micrograms plasmid DNA, 10 micrograms yeast tRNA, and 34-35% polyethylene glycol per 1 x 10(8) cells, Tn4001 could be introduced into M. pulmonis at a frequency of 5 x 10(-5) per colony forming unit. DNA-DNA hybridization studies illustrated that Tn4001 could occupy a diversity of insertion sites in the M. pulmonis chromosome. These data indicated that Tn4001 is a potentially useful tool for the introduction of mutations and for genetic studies in M. pulmonis.
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PMID:Random insertion of the gentamicin resistance transposon Tn4001 in Mycoplasma pulmonis. 254 7

Site-directed mutagenesis has been used to change the nucleotide C in the wobble position of tRNA(1Gly) (CCC) to U. The mutated tRNA was tested for its ability to read glycine codons in an in vitro protein-synthesizing system programmed with the phage message MS2-RNA that had been modified by site-directed mutagenesis so as to make it possible to monitor conveniently the reading of all four glycine codons. The results showed that while the efficiency of tRNA(1Gly) (UCC) was comparable to that of mycoplasma tRNA(Gly) (UCC) in the reading of the codon GGA, the mycoplasma tRNA(Gly) was far more efficient than the tRNA(1Gly) (UCC) in the reading of the codons GGU and GGC. Thus, the anticodon UCC, when present in the structural context of the tRNA(1Gly) molecule, behaved as predicted by the wobble rules while in the structural context of the mycoplasma tRNA(Gly) it read without discrimination between the nucleotides in the third codon position, in violation of the wobble restrictions. The result with the codon GGG showed that the anticodon UCC, when present in tRNA(1Gly), was considerably less efficient in reading this codon than it was in the structural context of the mycoplasma tRNA(Gly). It would therefore seem that the anticodon UCC, when present in a certain tRNA, can be an efficient wobbler, while in the molecular environment of another tRNA it is markedly restricted in its ability to wobble.
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PMID:Codon discrimination and anticodon structural context. 267 36

A physical map is presented for the 1200 kb genome of Mycoplasma mycoides subsp. mycoides Y, locating 32 cleavage sites for 8 restriction endonucleases. The large restriction fragments involved were separated and sized by pulsed-field agarose gel electrophoresis. Their locations on the map were determined by probing Southern blots of digests with individual fragments isolated from other digests and by correlating the products of double and triple digestions. Loci for 2 ribosomal RNA operons and 2 tRNA operons have been determined by probing with cloned genes and the broad regions of the replication origin and terminus have also been outlined by in vivo labelling studies.
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PMID:A physical map of the genome of Mycoplasma mycoides subspecies mycoides Y with some functional loci. 284 Jun 40

A transfer RNA complete devoid of modified nucleosides was synthesized by in vitro transcription, and some of its properties in aminoacylation and protein synthesis in vitro were studied. For this purpose, a plasmid was constructed which contained a glycine tRNA gene from Mycoplasma mycoides under the promoter of the T7 RNA polymerase, as well as a BstNI restriction site at the 3'-end of the tRNA gene. Cleavage of plasmid DNA with BstNI followed by T7 RNA polymerase transcription in vitro yielded an RNA which was processed with M1 RNA, the catalytic subunit of ribonuclease P, to give a tRNA of mature length. The tRNA synthesized in this manner can be esterified with glycine in vitro, and the rate of aminoacylation is the same as when using the corresponding fully modified glycine tRNA from M. mycoides. Furthermore, in protein synthesis in vitro, the tRNA lacking modified nucleosides was essentially as efficient as the corresponding normal glycine tRNA. However, the Escherichia coli extract used in our protein-synthesizing system introduced one modification, pseudouridine, into the in vitro-synthesized tRNA, and it cannot be excluded that this modification has an essential role in protein synthesis.
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PMID:Properties of a transfer RNA lacking modified nucleosides. 284 31

To investigate the organization of tRNA genes in the honeybee pathogen, Spiroplasma melliferum (previously referred to as Spiroplasma sp. BC3), total labeled tRNA from S. melliferum was used as a hybridization probe to an EcoRI digest of the genomic DNA. The results show two, or possibly three, strongly hybridizing bands. Comparing the pattern obtained to that of Bacillus subtilis DNA suggests either that the S. melliferum tRNA genes are more extensively clustered or, more likely, that the S. melliferum genome does not encode a full complement of tRNA genes, as has been suggested for other Mollicutes. We screened a library of EcoRI fragments of S. melliferum DNA cloned in pBR322 with total radioactive tRNA as a probe and selected one of the tRNA gene clusters. Subsequent sequence analysis of a portion of the clone showed 10 tRNA genes probably comprising a single operon. Comparison of sequence with a tRNA gene cluster from Mycoplasma mycoides and a portion of a cluster from B. subtilis showed an identical order of tRNA genes and the isoacceptors encoded. Such a striking comparison in gram-positive eubacteria suggests an important function for regulation and co-transcription of these tRNA genes.
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PMID:Organization and structure of tRNA genes in Spiroplasma melliferum. 311 24

The 5' region of the rRNA operon, rrnA, of M. capricolum was cloned. Sequence analysis revealed two tRNA genes, tRNA(leu) and tRNA(lys), upstream to the promoter of the rRNA operon. The in vivo transcription start sites of the rRNA operon and of the tRNA genes were mapped. The same promoters used by M. capricolum RNA polymerase are also recognized by E. coli RNA polymerase both in vivo and in vitro. We find that high levels of ppGpp in E. coli, resulting from amino acid starvation or from spoT mutation, activate rather than repress the transcription of the mycoplasma rrnA operon.
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PMID:Promoters of Mycoplasma capricolum ribosomal RNA operons: identical activities but different regulation in homologous and heterologous cells. 334 May 43

The transcription and RNA processing signals of the rRNA operons (rrnA and rrnB) of Mycoplasma capricolum were analyzed by mapping the 5' ends of in vivo and in vitro synthesized RNAs. The results of both in vitro and in vivo analyses point to the rrnA operon being transcribed from two promoters (P1 and P2) into large precursor RNAs. Transcripts initiating at P1 contain two tRNAs, and probably 16 S, 23 S, and 5 S rRNAs, whereas the transcripts starting from P2 consist only of the three rRNAs. The precursor RNAs are processed via distinct intermediates into mature tRNAs and rRNAs. In vivo experiments indicated that the rrnB operon is transcribed only from one promoter, although a second promoter could be identified using cell free extracts. The rrnB operon does not contain tRNA genes, but the precursor is still processed in the same way as the rrnA precursor that is synthesized from P2.
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PMID:Analysis of transcription and processing signals in the 5' regions of the two Mycoplasma capricolum rRNA operons. 341 21

Clues to evolution of the genetic code can be found by comparing usage of anticodons in various organisms and organelles. GC content of DNA varies, as a result of directional mutation pressure (AT/GC pressure), especially in bacteria. Low GC in Mycoplasma is accompanied by use of UGA for tryptophan and, in ciliated protozoa, by use of UAA and UAG for glutamine. These are examples of "stop codon capture," which has been preceded by duplication of tRNA genes followed by nucleotide substitutions in their sequences, including mutational changes in their anticodons. Evolutionary changes in the code may have resulted from disappearance of codons and anticodons resulting from GC pressure and from their reappearance when the direction of the pressure was reversed. In this manner, codon UGA and anticodon UCA for tryptophan could have disappeared under GC pressure and reappeared in Mycoplasma under AT pressure. Stop codon UGA may have been the third of the three stop codons to appear, originating from mutations in UAA. Changes in the code are adaptive and nondeleterious. We propose that the number of anticodons has increased and that evolution continued until three existing forms of the universal code were produced: eukaryotic, eubacterial, and the code for halobacteria and methanococci. These three codes are distinguished from each other by their anticodon pattern. The eukaryotic code contains eight INN (ANN) anticodons that have replaced GNN anticodons as a result of AT pressure. Mitochondrial and chloroplast codes have evolved from the eubacterial code through genomic economization and AT pressure, leading to losses of GNN and CNN anticodons.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Evolution of anticodons: variations in the genetic code. 345 89

The 16S and 23S rRNA genes of Mycoplasma hyopneumoniae are closely spaced in one operon. The two genes are separated by a spacer region of 500 bp which shows no sequence homology to bacterial tRNA genes. Within this operon seven 5' and five 3' ends of various rRNA species were mapped and the corresponding DNA was sequenced. The results are consistent with the following model for synthesis of rRNAs: Transcription of the operon is initiated from either of two tandemly arranged promoters leading to a large precursor RNA consisting of both 16S and 23S rRNAs. This primary transcript is first cleaved within stem structures surrounding the two rRNAs to yield premature 16S and 23S rRNAs. By further processing events the mature 5' and 3' ends are generated. The promoter sequences of this operon differ from those of other eubacterial promoters in lacking the typical -35 region. The putative termination site at the 3' end of the operon is reminiscent of rho-independent terminators in Escherichia coli.
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PMID:Analysis of transcription and processing signals of the 16S-23S rRNA operon of Mycoplasma hyopneumoniae. 347 May 91

Codon usage pattern in the threonine four-codon (ACN) box in Mycoplasma capricolum is strongly biased towards adenine and uracil for the third base of codons. Codons ending in uracil or adenine, especially ACU, predominate over ACC and ACG. This bacterium contains two isoacceptor threonine tRNAs having anticodon sequences AGU and UGU, both with unmodified first nucleotides. It would thus appear that ACN codons are translated in an unusual way; tRNA(Thr)(AGU) would translate the most abundantly used codon ACU exclusively, because adenine at the first anticodon position can, according to the wobble rule, pair only with uracil of the third codon position. The tRNA(Thr)(UGU) would mainly be responsible for translation of three other codons, ACA, ACG, and ACC. Anticodon UGU would also be used for reading codon ACU as a redundancy of tRNA(Thr)-(AGU), as deduced from the mitochondrial code where unmodified uracil at the first anticodon position can pair with adenine, cytosine, guanine, and uracil by four-way wobble. The tRNA(Thr)(AGU) has much higher sequence homology to tRNA(Thr)(UGU) from M. capricolum (88%), Bacillus subtilis (77%) and Escherichia coli (86%) than to tRNA(Thr)(GGU) from B. subtilis (66%) and E. coli (63%), suggesting that tRNA(Thr)-(AGU) has been derived from tRNA(Thr)(UGU), but not from tRNA(Thr)(GGU).
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PMID:Occurrence of unmodified adenine and uracil at the first position of anticodon in threonine tRNAs in Mycoplasma capricolum. 350 16


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