Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0348321 (Haemophilus)
 15,372 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Incorporation of the non-canonical amino acid selenocysteine into proteins requires the activity of the elongation factor SelB which substitutes for the function of EF-Tu in contrast to EF-Tu, SelB binds selenocystylated tRNASec and an mRNA secondary structure adjacent to the UGA selenocysteine codon. To gain information on the domain structure of this specialized translation factor, the selB genes from two bacteria unrelated to Escherichia coli (Clostridium thermoaceticum and Desulfomicrobium baculatum) were cloned and sequenced. The derived amino acid residue sequences were compared to those of SelB from E. coli and Haemophilus influenzae and to EF-Tu sequences. The alignment revealed that SelB contains all three domains characterized for EF-Tu. A fourth, C-terminally located domain shows only limited sequence conservation within the four SelB proteins. To elucidate the function of this C-terminal part a structure-function analysis of SelB from E. coli was performed. It showed that a C-terminal 17 kDa subdomain of the translation factor, when expressed separately, specifically binds the mRNA secondary structure. The recognition motif itself could be reduced to a 17 nucleotide minihelix without loss of binding affinity and specificity. A truncated SelB lacking the mRNA binding domain was still able to interact with selenocysteyl-tRNASec. Expression of the mRNA binding domain alone suppressed selenocysteine insertion in vivo by competing with SelB for its binding site at the mRNA. The results indicate that SelB can be considered as an EF-Tu homolog hooked to the mRNA via its C-terminal domain.
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PMID:Domain structure of the prokaryotic selenocysteine-specific elongation factor SelB. 889 53

Translation factor SelB is the key component for the specific decoding of UGA codons with selenocysteine at the ribosome. SelB binds selenocysteyl-tRNA(Sec), guanine nucleotides and a secondary structure of the selenoprotein mRNA following the UGA at the 3' side. A comparison of the amino acid sequences of SelB species from E. coli, Desulfomicrobium baculatum, Clostridium thermoaceticum and Haemophilus influenzae showed that the proteins consist of at least four structural domains from which the N-terminal three are well conserved and share homology with elongation factor Tu whereas the C-terminal one is more variable and displays no similarity to any protein known. With the aid of the coordinates of EF-Tu the N-terminal part has been modelled into a 3D structure which exhibits intriguing features concerning its interaction with guanine nucleotides and other components of the translational apparatus. Cloning and expression of fragments of SelB and biochemical analysis of the purified truncated proteins showed that the C-terminal 19 kDa protein fragment is able to specifically bind to the selenoprotein mRNA. SelB, thus, is a translation factor functionally homologous to EF-Tu hooked up to the mRNA with its C-terminal end. The formation by SelB of a quaternary complex in vivo has been proven by overexpression of truncated genes of SelB and by demonstration that fragments comprising the mRNA or the tRNA binding domain inhibit selenocysteine insertion.
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PMID:Domain structure of the selenocysteine-specific translation factor SelB in prokaryotes. 931 3