DNA Adenine Methylation Is Required to Replicate Both Vibrio cholerae Chromosomes Once per Cell Cycle

DNA adenine methylation is widely used to control many DNA transactions, including replication. In Escherichia coli, methylation serves to silence newly synthesized (hemimethylated) sister origins. SeqA, a protein that binds to hemimethylated DNA, mediates the silencing, and this is necessary to restrict replication to once per cell cycle. The methylation, however, is not essential for replication initiation per se but appeared so when the origins (oriI and oriII) of the two Vibrio cholerae chromosomes were used to drive plasmid replication in E. coli. Here we show that, as in the case of E. coli, methylation is not essential for oriI when it drives chromosomal replication and is needed for once-per-cell-cycle replication in a SeqA-dependent fashion. We found that oriII also needs SeqA for once-per-cell-cycle replication and, additionally, full methylation for efficient initiator binding. The requirement for initiator binding might suffice to make methylation an essential function in V. cholerae. The structure of oriII suggests that it originated from a plasmid, but unlike plasmids, oriII makes use of methylation for once-per-cell-cycle replication, the norm for chromosomal but not plasmid replication

The Stringent Response and Cell Cycle Arrest in Escherichia coli

The bacterial stringent response, triggered by nutritional deprivation, causes an accumulation of the signaling nucleotides pppGpp and ppGpp. We characterize the replication arrest that occurs during the stringent response in Escherichia coli. Wild type cells undergo a RelA-dependent arrest after treatment with serine hydroxamate to contain an integer number of chromosomes and a replication origin-to-terminus ratio of 1. The growth rate prior to starvation determines the number of chromosomes upon arrest. Nucleoids of these cells are decondensed; in the absence of the ability to synthesize ppGpp, nucleoids become highly condensed, similar to that seen after treatment with the translational inhibitor chloramphenicol. After induction of the stringent response, while regions corresponding to the origins of replication segregate, the termini remain colocalized in wild-type cells. In contrast, cells arrested by rifampicin and cephalexin do not show colocalized termini, suggesting that the stringent response arrests chromosome segregation at a specific point. Release from starvation causes rapid nucleoid reorganization, chromosome segregation, and resumption of replication. Arrest of replication and inhibition of colony formation by ppGpp accumulation is relieved in seqA and dam mutants, although other aspects of the stringent response appear to be intact. We propose that DNA methylation and SeqA binding to non-origin loci is necessary to enforce a full stringent arrest, affecting both initiation of replication and chromosome segregation. This is the first indication that bacterial chromosome segregation, whose mechanism is not understood, is a step that may be regulated in response to environmental conditions

Treatment Outcome Of Seizures Associated With Intracranial Cavernous Angiomas

Seizures are among the typical presentations of intracranial cavernous angiomas (ICA). Twenty-one patients (age range: 2 to 53 years) treated for seizures associated with ICA between 1983 and 1997 were restrospectively studied to evaluate their outcome following medical or surgical intervention. The mean interval between seizure onset and initial presentation at our institution was 7.6 years. Seizures were simple partial in 3 patients, complex partial in 15 and secondarily generalized tonic-clonic in 13. The commonest site of the lesion was the temporal lobe (52%). Multiple angiomas were observed in 5 (24%) patients. Seven (32%) patients were medically-managed with antiepileptic therapy and 14 (68%) underwent either lesionectomy with resection of the epileptogenic zone (9 patients) or temporal lobectomy (5 patients). Mean follow-up time was 4 years (range: 3 months to 14 years). Of the medically-managed patients, 3 (43%) remained seizure-free whereas 4 (57%) continued to have seizures with an average frequency of one per day. Of the surgically-managed patients, 12 (86%) became seizure-free and 2 (14%) had no more than two seizures per year. Surgery appears to be extremely effective in the management of seizures associated with ICA and should receive a strong and early consideration in patients who fail medical therapy

Impact of COVID-19 on routine immunisation in South-East Asia and Western Pacific: Disruptions and solutions.

10.1016/j.lanwpc.2021.100140Lancet Reg Health West Pac10100140