Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ermK gene from Bacillus lichenformis encodes an inducible rRNA methylase that confers resistance to the macrolide-lincosamide-streptogramin B antibiotics. The ermK mRNA leader sequence has a total length of 357 nucleotides and encodes a 14-amino acid leader peptide together with its ribosome binding site. The secondary structure of ermK leader mRNA and a leader peptide sequence have been reported as the elements that control expression. In this study, the contribution of specific leader peptide amino acid residues to induction of ermK was studied using the PCR-based megaprimer mutation method. ermK methylases with altered leader peptide codons were translationally fused to E. coil beta-galactosidase reporter gene. The deletion of the codons for Thr-2 through Ser-4 reduced inducibility by erythromycin, whereas that for Thr-2 and His-3 was not. The replacement of the individual codons for Ser-4, Met-5 and Arg-6 with termination codon led to loss of inducibility, but stop mutation of codon Phe-9 restored inducibility by erythromycin. Collectively, these findings suggest that the codons for residue 4, 5 and 6 comprise the critical region for induction. The stop mutation at Leu-7 expressed constitutively ermK gene. Thus, ribosome stalling at codon 7 appears to be important for ermK induction.
 ...
PMID:ErmK leader peptide : amino acid sequence critical for induction by erythromycin. 1722 66

Inhibitors of human immunodeficiency virus-1(HIV-1) proteinase have been used for several years to treat acquired immunodeficiency syndrome patients. Despite intensive research, however, the substrate specificity of this enzyme is not completely elucidated. Here, we assessed the HIV-1 proteinase P(4) to P(2) substrate specificity using a bacterial screening system. In this system, the bacterial enzyme beta-galactosidase has been transformed into an HIV-1 proteinase substrate by insertion of the p6/PR cleavage site. Consequently, HIV-1 processing can be determined by measuring the beta-galactosidase activity on X-gal plates and by examination of the extent of cleavage of the beta-galactosidase protein itself. We screened a library containing randomized sequences at the P(4) to P(2) positions and found strong preferences for Thr, Ser, and Pro at P(4), for Leu, Met, and Phe at P(3), and for Ser, Met, and Leu at P(2). The frequent observations of Thr at P(4) and Ser at P(2) extend previous findings and offer the possibility of producing inhibitors with different properties. These new data on HIV proteinase specificity illustrate the usefulness of random libraries in the genetic screening system. This approach can be applied to examine any proteinase that has a recognition site extending across several amino acids.
 ...
PMID:Investigating human immunodeficiency virus-1 proteinase specificity at positions P4 to P2 using a bacterial screening system. 1838 38


<< Previous 1 2 3 4