575 bp fragment by simultaneously digesting phix174 dna with hpych4v and with endonucleases which cleave at known positions such as clai nrui ndei and psti fig1 the approximate size of several of the dna fragments produced by hpych4v digestion of pbr322 dna was entered into the program sites gingeras et al nucl acids res 5 4105 1978 which generates potential recognition sequences for the input data by comparing the fragment sizes which would result from cleavage of the dna at any given recognition pattern with the input fragment sizes one such potential pattern generated was 5 39 tgca 3 39 which occurs in pbr322 dna at positions consistent with the mapping data obtained i e at positions 250 and 4037 the size of fragments predicted from cleavage at the sequence 5 39 tgca 3 39 in pbr322 puc19 and phix174 dnas matched the observed size of fragments from cleavage of these dnas with hpych4v from which we conclude that hpych4v recognizes the sequence 5 39 tgca 3 39 the point of cleavage within the hpych4v recognition sequence may be determined through dideoxy sequencing analysis of the terminal base sequence obtained from hpych4v cleavage of a suitable dna substrate sanger et al pnas 74 5463 5467 1977 brown et al j mol biol 140 143 148 1980 by the above referenced method fig2.