Terminus region of the chromosome in Escherichia coli inhibits replication forks.

Abstract

In the processes involved in the termination of replication of the circular chromosome of Escherichia coli, it has been determined that the replication terminus is opposite the replication origin and is located somewhere between the trp and his loci, but the position of the replication terminus has not yet been reported with any greater precision (1-4). It is also not certain if the replication terminus is a definite locus on the chromosome or if it is simply wherever the two replication forks involved in bidirectional replication happen to meet. Various investigators have reported results that suggest that replication occurs in a unidirectional fashion in certain situations (5-7). This suggests that there might not be a locus between the trp and his loci that blocks replication forks. Termination has now been studied with several different chromosomes that replicate bidirectionally, and the results demonstrate that bacteriophage X (8) and simian virus 40 (9) do not possess a specific region of the chromosome that blocks replication forks. The plasmid R6K, however, does have a terminus that blocks replication forks (10). The Bacillus subtilis chromosome might also have a specific terminus (11-13).In order to facilitate the study of termination in E. coli, we have sought conditions in which the normal symmetrical pattern of replication of the chromosome was altered so that one replication fork would reach the terminus region earlier than the other. We have recently determined that induction of prophage P2sig5 causes bacterial chromosome replication from the site of insertion of the prophage, and one of the strains we have studied has the prophage integrated near the terminus region. The results of studies of this strain are reported here. MATERIALS AND METHODSBacterial Strains and Media. PK241 is an F-thr leu his arg thi thyA drm dnaA malA+ E. coli strain derived from CRT4624. This latter strain and bacteriophage P2tsD4csigj (which will be called P2sig5 in this paper) were obtained from Y. Hirota (14). PK289 is an F-ilv arg met thi his thyA drm E. coli strain. PM 14 is a met trp his thr thy nic ilv Proteus mirabilis strain. The PM14 F' merogenote strains containing the F'129, F'116, F'111, F'101, and F'152 episomes were obtained by mating PM14 with E. coli strains containing these episomes and selecting for His+, Thy+, Ilv+, Thr+, and Gal+ cells, respectively. The E. coli F' strains were obtained from B. Bachman.The sources of the A specialized transducing phage were as follows: Xgt-E. coli EcoRI lop-li lig+ 1 (Alig), from R. Davis (15); XflaN+ 36 (Xfla), from M. Simon; A reverse (Arev), from M. Gellert (16); XptrpED 1 (Xtrp), from C. Yanofsky (17); XCIam34bio256 (Xbio), from M. Furth. XaroD was obtained by using the procedure of Schrenk and Weisberg (18).Cells were usually grown in M9 medium (19). During incubation in the absence of required amino acids, arginine or methionine was not removed from the medium. When PK241-P2-1 cells were labeled with 32P, they were grown in low-phosphate medium (20) containing 0.2...

Replication Termination inEscherichia coli: Structure and Antihelicase Activity of the Tus-TerComplex

“…It was found to terminate diametrically opposite oriC (between att80 at 28 min and attP2H at 45 min) even when the new origin was displaced by 26 min from it. Using a similar system, Kuempel et al (103,104) located the terminus between aroD and rac at 38 and 30 min, respectively, and Louarn et al (111) later reduced this interval to the 6 min between man and rac.…”

Microarray analysis of transposition targets in Escherichia coli : The impact of transcription

“…The E. coli chromosome replicates bidirectionally from the oriC to the terminus near the recombination sequence dif (19,20). Transposon Tn7 preferentially targets the terminus of replication (21).…”

DNA-protein interaction at the replication termini of plasmid R6K.

“…The termination of DNA replication of the chromosome of Escherichia coli and those of several of its plasmids occur at unique DNA sequences called replication termini (T) (Crosa et al 1976;Kuempel et al 1977: Louarn et al 1977Kolter and Helinski 1978;Bastia et al 1981a,b;Sista et al 1989). The termination process is interesting because of its potential as a biochemical coordination point or a linkage between a round of DNA replication and subsequent cell division.…”

“…Curiously, the T sites block the movement of the replication fork in a polarized fashion (Kuempel et al 1977;Koriuchi and Hidaka 1988;Sista et al 1989).…”