Product of T4 gene 12

Abstract

The product of gene 12 appears to be required for the proper functioning of the base plate of bacteriophage T4. Utilizing an in vitro assay for this gene product, a purification procedure has been devised. Gel filtration and sedimentation analyses show that the partially purified protein has a molecular weight of at least 157,000 daltons; in addition, a partially purified gene 12 product preparation activates purified gene 12 − particles at a high efficiency. Since other experiments have shown that the gene 12 product is a structural component of the phage, we interpret the high efficiency of activation to mean that the gene 12 product is the only structural defect of gene 12 − particles. Autoradiography of infected cell extracts analyzed by electrophoresis on sodium dodecyl sulfate/acrylamide gels reveals that the gene 12 polypeptide has a molecular weight of 55,000 daltons; moreover, this labeled polypeptide is the only peptide of molecular weight greater than ≈20,000 daltons which specifically binds to gene 12 − particles. We suggest that the 55,000 molecular weight polypeptide is the major subunit of the active gene 12 product and that the active protein contains at least two such peptides. The possibility of additional low molecular weight subunits has not been eliminated. Quantitative analysis of in vitro assembly, employing infected cell extracts, suggests that two gene 12 product molecules are capable of converting a gene 12 − particle to an infective unit but a gene 12 − particle possesses at least three binding sites for the gene 12 product. This product appears to “bind” to the debris present in infected cell extracts; the product of gene 11 does not.