Henthorn K S, Friedman D I
Department of Human Genetics, University of Michigan, Ann Arbor 48109, USA.
J Bacteriol. 1995 Jun;177(11):3185-90. doi: 10.1128/jb.177.11.3185-3190.1995.
Bacteriophage lambda grows in both IHF+ and IHF- host strains, but the lambdoid phage phi 80 and hybrid phage lambda (QSRrha+)80 fail to grow in IHF- host strains. We have identified a gene, rha, in the phi80 region of the lambda(QSRrha+)80 genome whose product, Rha, inhibits phage growth in an IHF- host. A search of the GenBank database identified a homolog of rha, ORF201, a previously identified gene in phage P22, which similarly inhibits phage growth in IHF- hosts. Both rha and ORF201 contain two possible translation start sites and two IHF binding site consensus sequences flanking the translation start sites. Mutations allowing lambda (QSRrha+)80 and P22 to grow in IHF- hosts map in rha and ORF201, respectively. We present evidence suggesting that, in an IHF+ host, lambda(QSRrha+)80 expresses Rha only late in infection but in an IHF- host the phage expresses Rha at low levels early in infection and at levels higher than those in an IHF+ host late in infection. We suspect that the deregulation of rha expression and, by analogy, ORF201 expression, is responsible for the failure of phi80, lambda(QSRrha+)80, and P22 to grow in IHF mutants.
噬菌体λ可在整合宿主因子（IHF）阳性和阴性的宿主菌株中生长，但类λ噬菌体φ80和杂交噬菌体λ（QSRrha +）80无法在IHF阴性宿主菌株中生长。我们在λ（QSRrha +）80基因组的φ80区域鉴定出一个基因rha，其产物Rha在IHF阴性宿主中抑制噬菌体生长。在GenBank数据库中搜索发现rha的一个同源物ORF201，它是噬菌体P22中一个先前已鉴定的基因，同样在IHF阴性宿主中抑制噬菌体生长。rha和ORF201都包含两个可能的翻译起始位点以及位于翻译起始位点两侧的两个IHF结合位点共有序列。使λ（QSRrha +）80和P22能在IHF阴性宿主中生长的突变分别位于rha和ORF201中。我们提供的证据表明，在IHF阳性宿主中，λ（QSRrha +）80仅在感染后期表达Rha，但在IHF阴性宿主中，噬菌体在感染早期低水平表达Rha，在感染后期表达水平高于IHF阳性宿主。我们推测rha表达以及类似的ORF201表达失调是导致φ80、λ（QSRrha +）80和P22无法在IHF突变体中生长的原因。
