[Cloning in Escherichia coli cells of mouse DNA fragments homologous to two main species of long hairpin regions of pre-mRNA].

Clones of plasmid pBR322, containing fragments of mouse DNA were obtained. DNA from many of these clones (at least 15%) was able to hybridize with double-stranded hairpin-like regions of pre-mRNA (dsRNA-B). It was shown by hybridization of dsRNA-B with clone DNA, that there are two abundant species of sequences in the population of these molecules designated as B1 and B2. They are 40-50% and 20-25% of all the molecule of dsRNA-B, respectively. The size of DNA sequences complementary to dsRNA is about 200--400 base pairs. The melting experiments with hybrids show that the members of B1 family are very similar if not identical, while the divergence among B2 sequences is higher but still the number of substitutions does not exceed 10% of bases. The sequence B1 and B2 are represented by many copies in the mouse genome and in pre-mRNA, and many of them probably do not form hairpin-like structures.