Gp32 Binding Research Articles

Nucleotide sequences involved in bacteriophage T4 gene 32 translational self-regulation.

We have determined the nucleotide sequence of a cloned segment of the bacteriophage T4D chromosome, which contains the regulatory sequences and the structural gene (gene 32) for the single-stranded DNA binding protein (gp32). The amino acid sequence predicted by translation of the structural gene agrees well with that published for gp32 [Williams, K. R., Lo-Presti, M. B., Setoguchi, M. & Konigsberg, W. H. (1980) Proc. Natl. Acad. Sci. USA 77, 4614-4617]. To localize the nucleotide sequence involved in translational self-regulation of gene 32, we have constructed a series of plasmids in which gene 32 is fused to an amino-terminal deletion mutant of the beta-galactosidase gene of Escherichia coli. Expression of a beta-galactosidase fusion protein that contains only the first seven amino acids of gp32 is still repressed by gp32. The ribosomal binding site of gene 32 is flanked by a repetitive A+T-rich sequence. Preferential and cooperative binding of gp32 to this region of its mRNA could inhibit translation initiation and, thus, would account for the autoregulation.

On the thermodynamics and kinetics of the cooperative binding of bacteriophage T4-coded gene 32 (helix destabilizing) protein to nucleic acid lattices

In this paper we summarize a series of thermodynamic, and preliminary kinetic, studies on the molecular details and specificity of interaction of phage T4-coded gene 32-protein (GP32) with nucleic acid lattices. It is shown that the binding of GP32 to short (l = 2--8 residues) oligonucleotides is essentially independent of base composition and sugar-type, as well as of salt concentration. In contrast, cooperative (continuous) or isolated binding of GP32 to single-stranded polynucleotides is base and sugar composition-dependent (binding is tighter to DNA than to RNA) and highly dependent on salt concentrations. Binding constants (K), cooperativity parameters (w), and binding site sizes (n) are determined for binding to various nucleic acid lattices under a variety of environmental conditions. These results are used to show that GP32 can bind to nucleic acid lattices in two different conformations, and to characterize the molecular details of these binding species. Further insight into the molecular origins of binding cooperativity is obtained by determining these thermodynamic parameters also for the specifically proteolytically degraded GP32 fragments GP32 I (C-terminal peptide removed) and GP32 III (C- and N-terminal peptides removed). It is also shown that these GP32-nucleic acid binding measurements can be used to provide a quantitative molecular interpretation of the sequential (competitive) binding equilibria involved in the autogenous translational regulation of GP32 synthesis (Lemaire et al., 1978, J. Mol. Biol. 126:73, 1978), and to illustrate some general principles of the development of interactional specificity in cooperatively binding protein-nucleic acid complexes. Preliminary experiments have also been carried out on the kinetics of GP32 association to, and dissociation from, single-stranded nucleic acid lattices. In particular, fluorescence stopped-flow measurements of the dissociation of GP32 from such lattices as a function of lattice saturation (and protein cluster size) can be interpreted to suggest that the protein may translocate ("slide") on the lattice before dissociation, These studies permit an approach to possible rates and mechanisms of such translocation events.