SUMMARY

By three different lines of evidence there are approximately 20 copies of actin genes in the human genome. Firstly, the rate of hybridisation of a mouse actin probe to human DNA indicates that there are a minimum of 20 complementary copies of the actin sequence per genome. Secondly, this probe hybridises to 17-20 bands in Southern blots of restriction enzyme digests of total human DNA. Most of these bands hybridise with both 31 and 5 ' fragments of the cDNA and are therefore likely to contain the entire gene sequence. Thirdly, we have picked 12 actin recombinants from a genomic library, and at the level of restriction enzyme mapping these represent nine different genes. Probability calculations indicate that these recombinants were picked from a pool of at least 20 different genes