PubMed · 9451326
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P Lheureux. 1998. Sensitivity, specificity, and predictive values.. https://doi.org/10.1016/s0735-6757(98)90077-8
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A novel function of initiation factors IF1 and IF2 in Escherichia coli translation has been identified. It is shown that these factors efficiently catalyse dissociation of peptidyl-tRNAs with polypeptides of different length from the P-site of E. coli ribosomes, and that the simultaneous presence of both factors is required for induction of drop-off. The factor-induced drop-off occurs with both sense and stop codons in the A-site and competes with peptide elongation or termination. The efficiency with which IF1 and IF2 catalyse drop-off decreases with increasing length of the nascent polypeptide, but is quite significant for hepta-peptidyl-tRNAs, the longest polypeptide chains studied. In the absence of IF1 and IF2 the rate of drop-off varies considerably for different peptidyl-tRNAs, and depends both on the length and sequence of the nascent peptide. Efficient factor-catalysed drop-off requires GTP but not GTP hydrolysis, as shown in experiments without guanine nucleotides, with GDP or with the non-cleavable analogue GMP-PNP.Simultaneous overexpression of IF1 and IF2 in vivo inhibits cell growth specifically in some peptidyl-tRNA hydrolase deficient mutants, suggesting that initiation factor-catalysed drop-off of peptidyl-tRNA can occur on a significant scale in the bacterial cell. Consequences for the bacterial physiology of this previously unknown function of IF1 and IF2 are discussed.
The gene encoding human biphenyl hydrolase-related protein (Bph-rp), a serine hydrolase with sequence similarity to prokaryotic enzymes involved in the degradation of polychlorinated biphenyls, has been cloned and its overall organization established. The gene, whose HGM-approved nomenclature is BPHL, spans more than 30 kb and is composed of eight exons and seven introns. The number and distribution of exons and introns differ from those reported for the genes encoding other serine hydrolases with sequence similarity to Bph-rp, indicating that these genes are distantly related. Nucleotide sequence analysis of the 5'-flanking region of BPHL revealed a high GC content, a ratio CpG/GpC close to unity, and the absence of consensus transcriptional sequences such as a TATA box or a CCAAT box. Chromosomal localization of BPHL revealed that it maps to chromosome 6p25, a unique location for all serine hydrolases mapped to date.
The partition behaviour of cutinase on poly(ethylene glycol) (PEG)-hydroxypropyl starch aqueous two-phase systems was characterized. The effect of molecular mass of PEG, the pH of the system and tie-line length on cutinase partition coefficient and cutinase yield to the top phase was investigated for systems prepared with a purified hydroxypropyl starch (Reppal PES 100) and a crude one (HPS). The effect of the presence of different salts, such as sodium chloride, sodium sulphate and ammonium sulphate, on cutinase partition was also studied. The results lead to the conclusion that aqueous two-phase systems composed of PEG and hydroxypropyl starch are not efficient in the purification of cutinase. In the majority of cases, the partition coefficients were very close to 1, with pH being the factor which affects most cutinase partition. Partition coefficients were significantly improved when salts were added to the systems. For PEG 4000-Reppal PES 100 [at pH 4.0; 0.5 M (NH4)2SO4], the partition coefficient for cutinase was 3.7, while a value of 12 was obtained for PEG 4000-HPS (at pH 4.0; 1 M NaCl). An isoelectric point (pI) of 7.8 was confirmed for cutinase by constructing a cross partition graphic from the results obtained in the experiments with different salts.