GTPase activity of bacteriophage T4 sheath protein.

We show by nuclear magnetic resonance studies that, following GTP hydrolysis during phage T4 sheath contraction, GDP remains bound to the sheath protein (gp18), whereas orthophosphate is released. gp18 in the contracted state has GTPase activity and can hydrolyse exogenous GTP; the reaction is calcium-dependent and displays high substrate specificity. The process comprises two steps: (1) displacement of GDP from gp18 by exogenous GTP, and (2) GTP hydrolysis proper. The first step appears to be rate-limiting and to be accelerated when the nucleotide-protein interaction is mechanically disrupted by sonication.

Formation of complexes between long tail fibres and substructural elements of phage T4D.

Complexes of substructural elements of bacteriophage T4 (baseplates, baseplate-core complexes) with long tail fibres were obtained for the first time by complementation in vitro. A study of the organization of the complexes was carried out by PAGE, electron microscopy and sedimentation analysis. About 90% of baseplates and baseplate-core complexes were combined with fibres. However, the number of the attached fibres varied from one to six. On the basis of the data obtained, we proposed that the attachment of long tail fibres can occur before the assembly of the whole bacteriophage.

On the presence of guanosine phosphate in the tail of bacteriophage T4.

Treatment of gp18, a biologically active monomer of the structural protein of the bacteriophage T4 contractile sheath, with 0.6 M-HClO4 leads to the release of GDP, GMP and inorganic phosphate. Each gp18 molecule is shown to carry three atoms of phosphorus. In the isolated protein preparation, gp18 and the nucleoside phosphate are in equimolar relation. It is suggested that in the native sheath-protein subunit, GDP and inorganic phosphate are united as GTP.