Mutational analysis of two structural genes of the temperate lactococcal bacteriophage TP901-1 involved in tail length determination and baseplate assembly

Two putative structural genes, orf tmp (tape measure protein) and orf bpp ( baseplate protein), of the temperate lactococcal phage TP901-1 were examine d by introduction of specific mutations in the prophage strain Lactococcus lactic ssp. cremoris 901-1. The adsorption efficiencies of the mutated phag es to the indicator strain L. lactic ssp. cremoris 3107 were determined and electron micrographs were obtained. Specific mutations in orf tmp resulted in the production of mostly phage head structures without tails and a few wild-type looking phages. Furthermore, construction of an inframe deletion or duplication of 29% in orf tmp was shown to shorten or lengthen the phage tail by approximately 30%, respectively. The orf tmp is proposed to functi on as a tape measure protein, TMP, important for assembly of the TP901-1 ph age tail and involved in tail length determination. Specific mutations in o rf bpp produced phages which were unable to adsorb to the indicator strain and electron microscopy revealed particles lacking the baseplate structure. The orf bpp is proposed to encode a highly immunogenic structural baseplat e protein, BPP, important for assembly of the baseplate. Finally, an assemb ly pathway of the TP901-1 tail and baseplate structure is presented. (C) 20 00 Academic Press.