Characterization of the dual start motif of a class II holin gene |
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Authors: | Maxim Barenboim Chung-Yu Chang Fadia dib Hajj & Ry Young |
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Institution: | Department of Biology, Texas A&M University, College Station, TX 77843, USA.,;Department of Microbiology, University of Texas, ESB 226, Austin, TX 78712-1095, USA.,;Pfizer Central Research, Eastern Point Road, Groton, CT 06340, USA.,;Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843-2128, USA. |
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Abstract: | Holins are small membrane proteins that, at a genetically programmed time in a bacteriophage infective cycle, allow bacteriolytic enzymes, or endolysins, to escape to the periplasm and to attack the cell wall. Most holins fall into two sequence classes, I and II, based on the number of potential transmembrane domains (three for class I and two for class II). The prototype class I holin gene, S λ, has a dual start motif and encodes not only the effector holin, Sλ105, but also an inhibitor, Sλ107, with a Met–Lys … extension at the terminus. The prototype class II holin gene of phage 21, S 21, begins with the motif Met–Lys–Ser–Met … , and a potential RNA secondary structure overlaps the Shine–Dalgarno sequence. Here, we demonstrate that (i) two protein products are elaborated from S 21, S2171 and S2168; (ii) the shorter product is required for lysis; (iii) the longer product, S2171, inhibits S 21 function; and (iv) the Lys-2 residue is important for the inhibitor function. Moreover, the RNA stem–loop structure is involved in the downregulation of S2171 synthesis. However, our results suggest that, in S 21, different segments of the single consensus Shine–Dalgarno sequence serve the two translational starts. These results show that the dual start motifs of class II holin genes are functionally homologous to those of class I holin genes. |
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