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

A method of microcloning, which involves microsurgical excision of chromoso me fragments, DNA amplification by means of a polymerase chain reaction (PC R), and ligation of amplified products with plasmids, was employed in study ing Drosophila polytene chromosomes for the first time. Clones of the DNA l ibrary 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 he terochromatin contained the 176 and 297 retrotransposons; the ninja retrotr ansposon characteristic of D. simulans; and two Drosophila repetitive eleme nts, ag and a12, the function of which remains unknown.