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71.
The rate of synonymous substitution in enterobacterial genes is inversely related to codon usage bias 总被引:31,自引:14,他引:31
Genes sequences from Escherichia coli, Salmonella typhimurium, and other
members of the Enterobacteriaceae show a negative correlation between the
degree of synonymous-codon usage bias and the rate of nucleotide
substitution at synonymous sites. In particular, very highly expressed
genes have very biased codon usage and accumulate synonymous substitutions
very slowly. In contrast, there is little correlation between the degree of
codon bias and the rate of protein evolution. It is concluded that both the
rate of synonymous substitution and the degree of codon usage bias largely
reflect the intensity of selection at the translational level. Because of
the high variability among genes in rates of synonymous substitution,
separate molecular clocks of synonymous substitution might be required for
different genes.
相似文献
72.
Jennifer H Humphreys Jessica AB van Nies Jackie Chipping Tarnya Marshall Annette HM van der Helm-van Mil Deborah PM Symmons Suzanne MM Verstappen 《Arthritis research & therapy》2014,16(6)
Introduction
This study aimed to investigate rheumatoid factor (RF) and anti-citrullinated protein antibody (ACPA) status and levels as predictors of mortality in two large cohorts of patients with early inflammatory arthritis (EIA).Methods
Data from the Norfolk Arthritis Register (NOAR) and Leiden Early Arthritis Clinic (EAC) cohorts were used. At baseline, patients had demographic data and smoking status recorded; RF, ACPA and inflammatory markers were measured in the local laboratories. Patients were flagged with national death registers until death or censor date. Antibody status was stratified as negative, low or high positive by RF and ACPA levels individually. In addition, patients were grouped as seronegative, RF positive, ACPA positive or double antibody (RF and ACPA) positive. Cox regression models explored associations between antibody status and mortality adjusting for age, sex, smoking status, inflammatory markers and year of enrolment.Results
A total of 4962 patients were included, 64% were female. Median age at onset was 56 (NOAR) and 54 (EAC) years. In NOAR and EAC respectively, 35% and 42% of patients were ACPA/RF positive. When antibody status was stratified as negative, low or high positive, there were no consistent findings between the two cohorts. Double antibody positivity was associated with excess mortality in both cohorts compared to seronegative patients: NOAR and EAC respective adjusted HR (95% confidence interval) 1.35 (1.09 to 1.68) and 1.58 (1.16 to 2.15).Conclusions
Patients with EIA who are seropositive for both RF and ACPA have increased mortality compared to those who are single positive or seronegative. Antibody level in seropositive patients was not consistently associated with excess mortality.Electronic supplementary material
The online version of this article (doi:10.1186/s13075-014-0483-3) contains supplementary material, which is available to authorized users. 相似文献73.
Molecular evolution of bacteriophages: evidence of selection against the recognition sites of host restriction enzymes 总被引:12,自引:0,他引:12
Restriction enzymes produced by bacteria serve as a defense against
invading bacteriophages, and so phages without other protection would be
expected to undergo selection to eliminate recognition sites for these
enzymes from their genomes. The observed frequencies of all restriction
sites in the genomes of all completely sequenced DNA phages (T7, lambda,
phi X174, G4, M13, f1, fd, and IKe) have been compared to expected
frequencies derived from trinucleotide frequencies. Attention was focused
on 6-base palindromes since they comprise the typical recognition sites for
type II restriction enzymes. All of these coliphages, with the exception of
lambda and G4, exhibit significant avoidance of the particular sequences
that are enterobacterial restriction sites. As expected, the sequenced
fraction of the genome of phi 29, a Bacillus subtilis phage, lacks Bacillus
restriction sites. By contrast, the RNA phage MS2, several viruses that
infect eukaryotes (EBV, adenovirus, papilloma, and SV40), and three
mitochondrial genomes (human, mouse, and cow) were found not to lack
restriction sites. Because the particular palindromes avoided correspond
closely with the recognition sites for host enzymes and because other
viruses and small genomes do not show this avoidance, it is concluded that
the effect indeed results from natural selection.
相似文献
74.