Isolation of homologous nuclear DNAs from sea-urchin embryos.

Studies are presented on the ability of low-molecular-weight nuclear DNA fractions to hybridize to higher-molecular-weight nuclear DNAs taken from different stages of early developing sea-urchin embryos, Strongylocentrotus purpuratus. Using preparative DNA-DNA hybridization, a fraction of 60-s mid-blastula DNA was isolated for its ability to anneal to 10-s morula DNA. Approximately 80 regions on each 60-s molecule were found to be homologous to 10-s DNA. High-molecular-weight (> 240-s) nuclear DNA from mesenchyme blastula stage and later stages (compared with DNA from pre-blastula nuclei) shows an increase in the number of regions homologous to fractions of 10and 60-s DNAs.