Four exons of a human homologue of a yeast cell division cycle gene (MCM6/mis5, which is thought to encode a DNA replication licensing factor) have been identified 3.3 kb upstream from the start of transcription of the intestinal lactase gene on human chromosome 2q21, initially by similarity to a rat 'intestinal crypt-cell replication factor'. RT-PCR analysis shows, that unlike lactase, MCM6 is not restricted in its tissue distribution and does not show person-to-person variation in the level of expression in adult intestine.