For the past ten months, we have attempted to locate the rI gene. To this end, we have sequenced seven open reading frames (ie, uncharacterized genes) in the nrdC.-tk region of the T4 genome of several purported rI mutants and compared their sequence to that of wild-type T4 and the Genbank T4 sequence of this region. Historically, the rI gene was one of the first genes to be mapped in the T4 genome and, along with rII and rIII, played a decisive role in the development of molecular genetics (circa 1950). However, over the past 40 years research concerning rI has lost impetus. Of the original three (rI, rII, rIII), rII was selected to detail fine genetic structure and elucidate the genetic code. Moreover, as other genes more essential to T4 infection were characterized, it became apparent that the rI gene was difficult to pin-point because of its physical location in the genome.

Nevertheless, some researchers (mainly in the T4 community) have remained interested in the rI gene and in ascertaining its role in the regulation of T4 lysis (ie, when T4 bursts out of an infected host cell). To date, we have found the apparent locus of the rI gene in the mobD.8 open reading frame (formerly named tk.-2), which maps between 59483 and 59193 in the T4 genome. This open reading frame is 291 nucleotides in length and presumably encodes a 97 amino acid protein with a molecular weight of 11,125 Da.

What remains somewhat of a mystery is that we have found mutations in mobD.8 in the five "classic" rI mutants (isolated in the 1940s), but not in a other presumed rI mutants isolated more recently. We feel fairly confident, however, that mobD.8 represents part, if not all, of what is canonically known as the rI gene.

Currently, we are attempting to investigate lysis inhibition. T4, unlike all other lytic phages, is capable of delaying the time at which it bursts out of an infected host cell. This process involves all of the r genes and perhaps a few others. And while it is known which T4 proteins are directly responsible for physically lysing host cells (ie the E lysozyme protein and the T pore-forming protein), all attempts at gaining insight into the molecular biology of the regulation of lysis have failed; and so it has remained a mystery for 40 years! In order to gain the first molecular insight into this process, we are hoping to find out when the t gene is transcribed into mRNA during infection. The t gene encodes a protein which forms a pore in the inner membrane of the host cell which allows T4 lysozyme to eat the cell wall, which in turn causes lysis. As a result, the t gene is the likely target for regulation when a delay in lysis occurs. Our investigation, probing when its mRNA is produced, will help determine if (and when) regulation of t occurs at the level of transcription.

The Canonical Locus of rI--an abstract from the 1996 T4 meeting.

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