HU and integration host factor function as auxiliary proteins in cleavage of phage lambda cohesive ends by terminase

Abstract

HU and iategrtion host factor (IHF) are small, basic heterodimeric DNA-binding proteins which participate in transcripion Intatin, DNA replication, and recom . We constructed isogenic Escherichia coli stains in which fIU, THF, or both proteins were absent. Bacteriophage X did not grow in hosts lacing both HU and THE. Phage DNA replication and late gene transcription were normal in the double mutants, but packaging of A DNA was defective. Mature phage DNA molecules were absent, indicating that terminase was unable to linearize K DNA. Phage variants carrying a small substitution near cos or the ohml mutation in the terminase gene, Nul, formed plaques on HU-IHF-strains. We propose that HU or THU is required to establish the higher-order DNA-protein structure at cos that is the substrate for K terminase.DNA-protein complexes with a high degree of organization form at the initiation of DNA replication and are intermediates in several DNA recombination reactions. The ordered structures arise from the concerted assembly of a number of proteins on supercoiled DNA and bring nucleotide sequences located at a distance or on separate molecules into close proximity. In some of these reactions, the DNA bending required to form the complexes is facilitated by low-molecular-weight basic DNA-binding proteins (reviewed by Travers [50]).The best-studied Escherichia coli proteins of this type are the integration host factor (IHF) and HU (reviewed by Drlica and Rouviere-Yaniv [7] and Friedman [14]). IHF is composed of two nonidentical subunits, a and ,B, encoded by the himA (32) and hip (12) genes, respectively. IHF binds in the DNA minor groove (54) and imparts a bend to the DNA in excess of 1400 (27,36,38,49). The binding of IHF to specific DNA sequences at the K attachment site promotes A integration and excision. In a role that is probably related to DNA bending, IHF bound at K promoters can inhibit (22) (10). Although k packaging can take place in THF-hosts, an absolute requirement for IHF can be seen when the phage carries a cos site mutation (cosl54 or cos59) (1,31) or when the host canries a DNA gyrase mutation (15). Phage carrying the ohml mutation in the Nul gene will form plaques on IHF-gyrB hosts (21; also see reference 9).The genes coding for the a and ,B subunits of HU, hupA and hupB, respectively, have recently been cloned (25,26

Evidence for involvement of proteins HU and RpoS in transcription of the osmoresponsive proU operon in Escherichia coli

“…(i) The dpeB (rpoS) mutation was identified in a selection for derivatives with reduced expression of the chromosomal proU+ operon. (ii) The present data on P1 regulation are consistent with the overlap that has been demonstrated between osmotic and stationary-phase responses for the promoters of several other loci in E. coli (15,(20)(21)(22) (8,19,26 (17,31,32), need to be understood in the context of the multiple mechanisms outlined in our model.…”

Virus DNA packaging: the strategy used by phage λ

“…This suggests that DNA bending by IHF facilitates co-operative interactions between terminase bound to R3 and terminases bound to R2/R1. In vivo studies indicate that the non-specific DNA-binding protein HU can also enhance DNA packaging, presumably by acting in a manner analogous to IHF (Mendelson et al, 1991). An interchangeability of IHF and HU in X site-specific recombination has also recently been demonstrated (Segall ef ai.…”

Action at a distance for glp repressor control of glpTQ transcription in Escherichia coli K‐12

“…Plasmid pUHS2 (a kanamycin-resistant (Kan R ) pSC101 derivative; R. Lutz and H. Bujard, University of Heidelberg) was introduced into the parent strains by selection for Kan R . The resulting transformants were used as recipients in P1 crosses with strain A5427 (⌬ihfA82:Tn10; Mendelson et al (1991) …”

“…Transductants containing the ihfA deletion (Table 4) were identified by their kanamycin-sensitive phenotype (replication of plasmids with the pSC101 origin requires IHF; Cohen and Chang (1973); Pagel and Hatfield (1991)). To construct strains lacking HU, two consecutive P1 transductions were performed with strain A5427 (hupA16 ::kan hupB11::cat ; Mendelson et al (1991)) as donor and Kan R followed by selection for chloramphenicol resistance (Table 4).…”