1.E.28 The Streptomyces aureofaciens Phage Mu1/6 Holin (Mu1/6 Holin) Family
Two genes, designated, lyt and hol, are in the lysis module of phage mu1/6. An additional candidate holin gene, hol2, is encoded downstream from the hol gene based on one predicted transmembrane domain and a highly charged C-terminal sequence. Expression of hol or hol2 in E. coli caused cell death. The concomitant expression of lambda endolysin (R) and mu1/6 holin resulted in cell lysis. Similarly, the coexpression of the endolysin and holin of phage mu1/6 led to lysis, apparently due to the ability of mu1/6 endolysin to hydrolyze the peptidoglycan layer of this bacterium (Farkasovská and Godány 2008). In contrast, the simultaneous expression of mu1/6 hol2 and the endolysin gene (lambdaR or mu1/6 lyt) did not cause lysis. Demonstration of the holin function in Streptomycetes was achieved by allowing release of mu1/6 endolysin to the periplasm and subsequent cleavage of the peptidoglycan. Thus, the holin produces lesions in the streptomycete membrane.