PARTIAL RECONSTRUCTION OF THE LAMPBRUSH LOOP PAIR NOOSES ON THE Y-CHROMOSOME OF DROSOPHILA-HYDEI

We present the analysis of genomic DNA fragments that were isolated as potential segments of the lampbrush loop pair Nooses on the short arm of the Y chromosome of Drosophila hydei. More than 300 kb of DNA were recovered in BamHI lambda and cosmid clone groups. This DNA is compos ed of the Y-specific ay1 family of repetitive DNA sequences, and of ot her repetitive DNA sequences, which at least in pari are also located elsewhere in the genome (Y-associated sequences). Two additional class es of DNA fragments were obtained from an EcoRI library. One of them c onsists of ay1 repeats without apparent interspersion, including a tot al of more than 300 kb of DNA. The other is composed of tandemly repea ted YsI sequences, a Y-specific sequence derived from ay1. This class includes more than 400 kb of DNA, which is also not interspersed by ot her sequences. Our results show that only the ay1 repeats interspersed by Y-associated DNA sequences can represent parts of the 260 kb trans cription unit forming the lampbrush loop, whereas the ay1 and YsI repe ats without interspersion form separate and nontranscribed clusters of repetitive DNA.