Using transposon Tn5 insertions to sequence bacteriophage T4 gene 11

Structure of bacteriophage T4 gene product 11, the interface between the baseplate and short tail fibers

Bacteriophage T4, like all other viruses, is required to be stable while being transmitted from host to host, but also is poised to eject efficiently and rapidly its double-stranded DNA genome to initiate infection. The latter is coordinated by the recognition of receptors on Escherichia coli cells by the long tail fibers and subsequent irreversible attachment by the short tail fibers. These fibers are attached to the baseplate, a multi-subunit assembly at the distal end of the tail. Recognition and attachment induce a conformational transition of the baseplate from a hexagonal to a star-shaped structure. The crystal structure of gene product 11 (gp11), a protein that connects the short tail fibers to the baseplate, has been determined to 2.0 A resolution using multiple wavelength anomalous dispersion with Se. This structure is compared to the trimeric structure of gp9, which connects the baseplate with the long tail fibers. The structure of gp11 is a trimer with each monomer consisting of 218 residues folded into three domains. The N-terminal domains form a central, trimeric, parallel coiled coil surrounded by the middle "finger" domains. The fingers emanate from the carboxy-terminal beta-annulus domain, which, by comparison with the T4 whisker "fibritin" protein, is probably responsible for trimerization. The events leading from recognition of the host to the ejection of viral DNA must be communicated along the assembled trimeric (gp9)(3) attached to the long tail fibers via the trimeric baseplate protein (gp10)(3) to the trimeric (gp11)(3) and the trimeric short tail fibers.

Identification of bacteriophage T4 virion proteins by transverse pore-gradient sodium dodecyl sulfate-polyacrylamide gel electrophoresis and dual amino acid labeling

We have developed a horizontal N,N'-methylenebisacrylamide (Bis) acrylamide gradient sodium dodecyl sulfate (SDS) gel system that permits the evaluation of the purity of individual protein bands in complex mixtures. A Bis gradient gel is poured vertically and, after polymerization, reoriented horizontally. A single large sample spanning the top of the gel is then run down at right angles to the gradient. The relative mobility of a few proteins varies considerably from the rest, causing them to merge with and cross other bands as the Bis concentration changes. Band splitting revealed that several bands previously thought to represent a single species are actually comprised of comigrating proteins. Once the Bis/monomer concentration offering the best separation was identified, we sought a simple method for identifying the genetic origin of bands, since many proteins now migrated in new positions on the gel. We reasoned that if infected cells were simultaneously labeled with [35S]methionine and [3H]leucine and the purified virion proteins analyzed to determine their 35S/3H ratio, we could identify most proteins by comparing this ratio with one calculated from the T4 DNA sequence. Our expectations were realized, and we here report the separation and identification of all T4 virion proteins. Finally, we comment on the incorporation of various changes to the original Laemmli SDS-polyacrylamide gel formulations that have been reported in the literature.

Cloning and molecular analysis of genes affecting expression of binding substance, the recipient-encoded receptor(s) mediating mating aggregate formation in Enterococcus faecalis

Transfer of the conjugative plasmid pCF10 in Enterococcus faecalis strains involves production of a plasmid-encoded aggregation substance on the surface of donor cells in response to stimulation by a pheromone secreted by recipient cells. Aggregation substance then facilitates attachment to recipient cells via a chromosomally encoded receptor, termed binding substance (BS). A BS mutant, strain INY3000, generated by random Tn916 insertions, was previously found to carry copies of the transposon at four unique sites (K. M. Trotter and G. M. Dunny, Plasmid 24:57-67, 1990). In the present study, DNA flanking the Tn916 insertions was used to complement the BS mutation of INY3000 following Tn916 excision from cloned chromosomal fragments. Complementation results showed that three of the four regions mutated in INY3000 play some role in BS expression. Tn5 mutagenesis and DNA sequence analysis of the complementing fragment from one of these regions indicated the presence of three genes (ebsA, ebsB, and ebsC) that affect BS expression. The ebsA and ebsB genes encode peptides likely to function in cell wall metabolism, whereas ebsC may encode a product that suppresses the function or expression of EbsB.

Transposon-facilitated DNA sequencing

We describe here a transposon-based DNA sequencing strategy that allows the introduction of sequencing priming sites throughout a target sequence by bacterial mating. A miniplasmid was designed to select against transposon insertions into the vector. Sites of transposon insertion are mapped by the polymerase chain reaction with bacterial overnight cultures providing the templates. A small set of plasmids with transposons spaced several hundred base pairs apart can then be sequenced. Sequencing primers corresponding to the transposon ends allow sequencing in both directions. Thus, the entire sequence of both strands can be easily determined.