Microcloning and characterization of DNA from pericentromeric heterochromatin of Drosophila melanogaster polytene chromosomes

A method of microcloning, which involves microsurgical excision of chromosome fragments, DNA amplification by means of a polymerase chain reaction (PCR), and ligation of amplified products with plasmids, was employed in studying Drosophila polytene chromosomes for the first time. Clones of the DNA library thus obtained contained inserts varying in size from 0.1 to 0.5 kb. DNA sequencing of five clones of the library showed that pericentromeric heterochromatin contained the 176 and 297 retrotransposons; the ninja retrotransposon characteristic of D. simulans; and two Drosophila repetitive elements, ag and a12, the function of which remains unknown