Nucleic Acids Research Advance Access published online on June 15, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp504
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Molecular Biology |
Differential Spo0A-mediated effects on transcription and replication of the related Bacillus subtilis phages Nf and 
29 explain their different behaviours in vivo
Instituto de Biología Molecular ‘Eladio Viñuela’ (CSIC), Centro de Biología Molecular ‘Severo Ochoa’ (CSIC-UAM), C/Nicolás Cabrera 1, Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain
*To whom correspondence should be addressed. Tel: +34 91 196 4675; Fax: +34 91 194 4677; Email: msalas{at}cbm.uam.es
Correspondence may also be addressed to Wilfried J.J. Meijer. Tel: +34 91 196 4515; Fax: +34 91 194 4420; Email: wmeijer{at}cbm.uam.es
Received February 10, 2009. Revised May 22, 2009. Accepted May 25, 2009.
Members of groups 1 (e.g. 
29) and 2 (e.g. Nf) of the 29 family of phages infect the spore forming bacterium Bacillus subtilis. Although classified as lytic phages, the lytic cycle of 29 can be suppressed and its genome can become entrapped into the B. subtilis spore. This constitutes an alternative infection strategy that depends on the presence of binding sites for the host-encoded protein Spo0A in the 29 genome. Binding of Spo0A to these sites represses 29 transcription and prevents initiation of DNA replication. Although the Nf genome can also become trapped into B. subtilis spores, in vivo studies showed that its lytic cycle is less susceptible to spo0A-mediated suppression than that of 29. Here we have analysed the molecular mechanism underlying this difference showing that Spo0A differently affects transcription and replication initiation of the genomes of these phages. Thus, whereas Spo0A represses all three main early promoters of 29, it only represses one out of the three equivalent early promoters of Nf. In addition, contrary to 29, Spo0A does not prevent the in vitro initiation of Nf DNA replication. Altogether, the differences in Spo0A-mediated regulation of transcription and replication between 29 and Nf explain their different behaviours in vivo.