A spontaneous insertion of an early transposon sequence (ETn) in intron 4 of the gene was detected by Southern blot analysis and by sequencing. Northern blot analysis on RNA derived from spleen tissue of homozygous mice did not detect a wild-type size transcript, but trace amounts of a larger transcript were detected. Reduced hexokinase activity was shown functionally in red blood cells, spleen and kidney. (J:72146)