coli causes cellular lysis after permeabilization of the plasma membrane with chloroform (Henrich et al., 1995; Chandry et al., 1997; Garcia et al., 2002). Figure 4a portrays the decrease in OD600 nm observed following the addition of chloroform 1 h after induction. HDAC inhibitor The reduction in OD600 nm for the gp29-containing clones was significantly greater than the control (P<0.05) (Fig. 4a). Zymograms were performed to examine the ability of gp29 to hydrolyse peptidoglycan. A clear band appeared on the blue background after shaking in distilled water after 48–72 h at room temperature postrenaturation, indicating the lysis of M. lysodeikticus. The molecular weight was determined to be approximately

58 kDa, which was as expected for TM4 gp29 protein based on in silico analysis (Fig. 4b). A clear band was also seen at an approximate molecular weight of 15 kDa for the lysozyme positive control (data not shown). The clearing appeared for the crude lysate, the purified fractions as well as postconcentration and postdesalting samples (Fig. 4b). Hatfull et al. (2006) examined the complete sequences of 30 mycobacteriophage genomes and suggested that gp29 of TM4 may encode a lysin A protein. Our bioinformatic analyses further supports this hypothesis by revealing that the putative protein encoded by gp29 possesses a peptidoglycan-recognition GSK-3 inhibitor review domain common to other previously characterized lysin

A proteins. In order to investigate the function of the protein encoded by gp29, it was decided to clone and heterologously express it in E. coli using the pQE60 expression system. Cloning was successful and conditions for expression of gp29 protein were optimized. Preliminary assays showed killing of the E. coli pQE60+gp29 clones after the inner membrane was permeabilized with chloroform, thus supporting the 17-DMAG (Alvespimycin) HCl initial hypothesis that gp29 encodes a protein capable of degrading the bacterial peptidoglycan. This result is consistent with those of other studies, in which the overexpression of phage lysins does not inhibit E. coli growth unless chloroform has been added (Henrich et al., 1995; Chandry et al.,

1997), therefore supporting the initial assumption that TM4_gp29 gene (gp29) encodes a lysin with mureinolytic activity. This has also been observed for another mycobacteriophage lysin (Ms6 gp2) (Garcia et al., 2002), which led to the identification of Ms6 lysin A gene. Following zymogram analysis, degradation of the peptidoglycan occurred at a zone of approximately 58 kDa (predicted size of gp29). The clear band was observed for crude lysate as well as for the purified desalted fraction, showing that activity is retained through the purification process as well as through the concentration and desalting steps. This result demonstrates the presence of a cell wall-degrading enzyme within the mycobacteriophage TM4 genome and further supports the hypothesis that TM4gp29 is the lysin A of this mycobacteriophage.