ANALYSIS OF THE BACILLUS-SUBTILIS BACTERIOPHAGE-SPP1 AND BACTERIOPHAGE-SF6 GENE-1 PRODUCT - A PROTEIN INVOLVED IN THE INITIATION OF HEADFULPACKAGING

Gene I product (GIP) of the related Bacillus subtilis bacteriophages S PP1, SF6, and rho 15 is essential for DNA maturation and packaging. A DNA segment containing gene 1 of phage SF6 or rho 15 origin was cloned and sequenced. SF6 and rho 15 G1P (both with predicted molecular mass of 16.7 kDa) share 71% identity with G1P of SPP1. The G1P of all thre e phages contains three conserved segments (I, II, and III). Within se gments I and II helix-turn-helix DNA binding and nucleotide binding mo tifs were predicted. G1P of both SPP1 and SF6 origin was purified. SPP 1 G1P protein (20.7 kDa), purified from cells overexpressing the clone d gene, purifies together with another polypeptide, having a molecular mass of about 13 kDa. The 13-kDa polypeptide results from a translati on start signal within gene 1, and hence was termed SPP1 G1P. G1P of both SPP1 and SF6 binds specifically to a pac-containing DNA fragment, whereas G1P, which lacks segment I, does not. Chimeric G1P protiens were obtained by domain swapping between gene I of SPP1 and SF6. The r esults presented here suggest that the G1P DNA binding motif lies in s egment I and the major determinant for G1P::G1P interaction might lie in segment II. Segment III and the extended C-terminal part of SPP1 G1 P are dispensable. The G1P::G2P interacting region remains uncharacter ized. (C) 1994 Academic Press, Inc.