Nucleic Acids Research

Cover.

The structure of bacteriophage T4 polynucleotide kinase domain, bound to a single-stranded DNA substrate fragment, illustrates its mechanism of non-specific binding and phosphorylation of nucleic acids. The DNA substrate (pink atoms) is bound in a surface cleft on the kinase domain (shown as a green ribbon diagram with an overlaid molecular surface). The 5 ribose phosphate acceptor points into an active site tunnel, towards a bound nucleotide phosphate donor (light purple, buried within the protein). The DNA is bound with its backbone contacting the protein surface and the corresponding bases extending towards solution. Variable stacking arrangements between the first three bases at the 5 end of the DNA contribute to the substrate sequence preferences displayed by the enzyme. For further details see the paper by Eastberg et al. in this issue [Nucleic Acids Res. (2004) 32, 653-660].