Kinetics of transcription initiation at lacP1: multiple roles of cyclic amp receptor protein

The cyclic AMP receptor protein (CRP) acts as a transcription activator at many promoters of Escherichia coli. We have examined the kinetics of open complex formation at the lacP1 promoter using tryptophan fluorescence of RNA polymerase and DNA fragments with 2-aminopurine substituted at specific positions. Apart from the closed complex formation and promoter clearance, we were able to detect three steps. The first step after the closed complex formation leads to a rapid increase of 2-aminopurine fluorescence. This was followed by another rapid step in which quenching of tryptophan fluorescence of RNA polymerase was observed. The slowest step detected by 2-aminopurine fluorescence increase is assigned to the final open complex formation. We have found that CRP not only enhances RNA polymerase binding at the promoter, but also enhances the slowest isomerization step by about 2-fold. Furthermore, potassium permanganate probing shows that the conformation of the open complex in the presence of CRP appears qualitatively and quantitatively different from that in the absence of CRP, suggesting that contact with RNA polymerase is maintained throughout the transcription initiation

Risk of tuberculosis after initiation of antiretroviral therapy among persons with HIV in Europe.

OBJECTIVES Tuberculosis (TB) risk after initiation of antiretroviral treatment (ART) is not well described in a European setting, with an average TB incidence of 25/105 in the background population. METHODS We included all adult persons with HIV starting ART in the RESPOND cohort between 2012 and 2020. TB incidence rates (IR) were assessed for consecutive time intervals post-ART initiation. Risk factors for TB within 6 months from ART initiation were evaluated using Poisson regression models. RESULTS Among 8441 persons with HIV, who started ART, 66 developed TB during 34,239 person-years of follow-up [PYFU], corresponding to 1.87/1000 PYFU (95% confidence interval [CI]: 1.47-2.37). TB IR was highest in the first 3 months after ART initiation (14.41/1000 PY (95%CI 10.08-20.61]) and declined at 3-6, 6-12, and >12 months post-ART initiation (5.89 [95%CI 3.35-10.37], 2.54 [95%CI 1.36-4.73] and 0.51 [95%CI 0.30-0.86]), respectively. Independent risk factors for TB within the first 6 months after ART initiation included follow-up in Northern or Eastern Europe region, African origin, baseline CD4 count 100,000 copies/mL, injecting drug use and heterosexual transmission. CONCLUSIONS TB IR was highest in the first 3 months post-ART initiation and was associated with baseline risk factors, highlighting the importance of thorough TB risk assessment at ART initiation

Integrase Strand Transfer Inhibitor Use and Cancer Incidence in a Large Cohort Setting

Background: Limited data exist examining the association between incident cancer and cumulative integrase inhibitor (INSTI) exposure. Methods: Participants were followed from baseline (latest of local cohort enrollment or January 1, 2012) until the earliest of first cancer, final follow-up, or December 31, 2019. Negative binomial regression was used to assess associations between cancer incidence and time-updated cumulative INSTI exposure, lagged by 6 months. Results: Of 29 340 individuals, 74% were male, 24% were antiretroviral treatment (ART)-naive, and median baseline age was 44 years (interquartile range [IQR], 36-51). Overall, 13 950 (48%) individuals started an INSTI during follow-up. During 160 657 person-years of follow-up ([PYFU] median 6.2; IQR, 3.9-7.5), there were 1078 cancers (incidence rate [IR] 6.7/1000 PYFU; 95% confidence interval [CI], 6.3-7.1). The commonest cancers were non-Hodgkin lymphoma (n=113), lung cancer (112), Kaposi's sarcoma (106), and anal cancer (103). After adjusting for potential confounders, there was no association between cancer risk and INSTI exposure (≤6 months vs no exposure IR ratio: 1.15 [95% CI, 0.89-1.49], >6-12 months; 0.97 [95% CI, 0.71-1.32], >12-24 months; 0.84 [95% CI, 0.64-1.11], >24-36 months; 1.10 [95% CI, 0.82-1.47], >36 months; 0.90 [95% CI, 0.65-1.26] [P=.60]). In ART-naive participants, cancer incidence decreased with increasing INSTI exposure, mainly driven by a decreasing incidence of acquired immune deficiency syndrome cancers; however, there was no association between INSTI exposure and cancer for those ART-experienced (interaction P<.0001). Conclusions: Cancer incidence in each INSTI exposure group was similar, despite relatively wide CIs, providing reassuring early findings that increasing INSTI exposure is unlikely to be associated with an increased cancer risk, although longer follow-up is needed to confirm this finding

Cyclic AMP-induced conformational change of cyclic AMP receptor protein (CRP): intragenic suppressors of cyclic AMP-independent CRP mutations.

We isolated and characterized crp mutations in Escherichia coli that allow cyclic AMP (cAMP) receptor protein to function without cAMP. These mutants defined a region involved in the cAMP-induced allosteric change of cAMP receptor protein that is necessary for activation of the protein. Currently, we have isolated intragenic suppressors of the crp mutations. These crp (Sup) mutants require cAMP for activity. The crp (Sup) mutations map in regions which define new sites of changes involved in cAMP receptor protein activation. From these results, we suggest that to activate cAMP receptor protein cAMP brings about (i) a hinge reorientation to eject the DNA-binding F alpha-helices, (ii) proper alignment between the two subunits, and (iii) an adjustment between the position of the two domains. Cyclic GMP fails to effect the last step