Temporal and spatial regulation of cell division by the nucleoid in Escherichia coli

Selection of division sites and coordination of cytokinesis with other cell cycle events are critical for every organism to proliferate. In E. coli, the nucleoid is proposed to exclude division from the site of the chromosome (nucleoid occlusion model). We studied the effect of the nucleoid on timing and placement of cell division. An early cell division protein, FtsZ, was used to follow development of the division septum. FtsZ forms a ring structure (Z ring) at potential division sites. The dynamics of Z ring was visualized in live cells by fusing FtsZ with a green fluorescent protein (GFP). Emanating FtsZ-GFP polymers from the constricted septum or aggregates in daughter cells were also observed, probably representing the FtsZ depolymerization and immature FtsZ nucleation processes. We next examined the nucleoid occlusion model. Mutants carrying abnormally positioned chromosomes were employed. In chromosomal partition mutants, replicated chromosomes cannot segregate. The Z ring was excluded from midcell to the edge of the nucleoid. This negative effect of nucleoids was further confirmed in replication deficient dnaA mutants, in which only a single chromosome is present in the cell center. These results suggest that the nucleoid, replicating or not, inhibits division in the area where the chromosome occupies. In addition, increasing the level of FtsZ does not overcome nucleoid inhibition. Interestingly in anucleate cells produced by both mutants, the Z ring was localized in the central part of the cell, which indicates that the nucleoid is not required for FtsZ assembly. Relaxation of chromosomes by reducing the gyrase activity or disruption of protein translation/translocation did not abolish the division inhibition capacity of the nucleoid. However, preventing transcription did compromise the nucleoid occlusion effect, leading to formation of multiple FtsZ rings above the nucleoid. In summary, we demonstrate that nucleoids negatively regulate the timing and position of division by inhibiting FtsZ assembly at unselected sites. Relief of this inhibition at midcell is coincident with the completion of DNA replication. On the other hand, FtsZ assembly does not require the nucleoid. ^

Internet as a medium to seek partners among men who have sex with men

While there are reports of developing sexual relationships on the Internet (I) among MSM, there are few reports that have examined the process of developing sexual relationships on the I and comparing to that in real life (IRL). This study examines the process to provide insight into how MSM make decisions about courtship, engages in negotiations for sex, and choose sexual partners and examines the comparative sexual risks taken between I vs. IRL negotiation. This self-selected convenience sample at a national level (n=1001) of MSM recruited through the I, systematically explored the different steps, the process of courtship in a flow chart of I and IRL dating to portray the process of filtering, courtship and/or negotiation for sex. Risk behaviors in both environments are presented along with interactions that create predictable sequences or "scripts". These sequences constitute 'filtering' and 'sexual positioning'. Differences between I & IRL suggest discussion of HIV/STD status to have consistent differences for all variables except 'unprotected sex' meaning no condom use. There was more communication on the I in regards to self revealing information or variables relating to reducing risks which enable 'filtering' (including serosorting). Data indicate more steps in the I process, providing more complex, multiple steps to filter and position with regard not only to HIV/STD risk but also to negotiate position for complementary sexual interest. The study established a pattern of MSM's courtships or negotiation for sex and a pattern of acquisition, and more I negotiation. Data suggest negotiation opportunities which could lend to intervention to advise people how to negotiate safely. ^ Previous studies have reviewed MSM and drug use. This is a study to review the process of drug use associated with sexual behavior regarding the Internet (I) and in real life (IRL) using a self-selected, convenience sample of MSM (n=1001) recruited nation-wide through the Internet. Data on MSM and drugs illustrate the Internet being used as a tool to filter for drug use among MSM. MSM's drug use in both environments highlights the use of sexual performance drugs with an IRL pursuit of intimacy or negotiation for sex. IRL encounters were more likely to involve drug use (both recreational and sexual performance-enhancing) than Internet encounters. This may be due to more IRL meetings occurring at bars, clubs or parties where drug use is a norm. Compared with IRL, the Internet may provide a venue for persons who do not want to use drugs to select partners with similar attitudes. This suggests that filtering may be occurring as part of the internet negotiation. Data indicated that IRL persons get drunk/high before having sex in past 60 days significantly more often than Internet participants. Age did not alter the pattern of results. Thus drug filtering is really not recreational drug filtering or selecting for PNP, but appears to be situationally-based. Thus, it should perhaps be seen as another form of filtering to select drug-free partners, rather than using the Internet to specifically recruit and interact with other recreational drug users. ^