Start sites of bidirectional DNA synthesis at the human lamin B2 origin

The initiation sites of bidirectional synthesis at the DNA replication orig in located at the 3' end of the human lamin B2 gene were investigated. RNA- primed nascent DNA molecules were subjected to second-strand synthesis with appropriate primers, amplified by ligation-mediated polymerase chain react ion, and size fractionated. Evidence for precise start sites was obtained. Exploration of close to 1 kilobase, coupled to inhibition of Okazaki fragme nt synthesis, demonstrates that the leading strands initiate at precise nuc leotides on either helix, overlapping by three base pairs, within the area bound to a protein complex possibly analogous to the prereplicative complex of yeast.