Genes 16 and 17 of phage T4 encode two proteins, gp (gene product) 16 and gpl7, required to translocate phage T4 DNA into the head (1, 2, 3). We have determined the DNA sequence of these genes from random and restriction T4 fragments cloned into M13 or various plasmids. The two genes overlap (out-offrame) as indicated. The molecular weights of the proteins, deduced from the DNA sequence (18,367 for gpl6; 69,677 for gpl7) agree with those determined from polyacrylamide gel electrophoresis (3). The correspondence of various clones to genes 16 or 17 was confirmed by marker rescue experiments. The beginning of our sequence overlaps with the last 207 nucleotides of the genes 13, 14 and 15 sequence (4). Several discrepancies in that sequence compared with ours, obliterated the initiation codon for gpl6 whose function we confirmed by complementation of a gene 16 mutant. The end of gene 17 overlaps with the'gene 18 promoter (5). ACKNOWLEDGEMENTS