Characterization of a family of repetitive sequences that is eliminated late during macronuclear development of the hypotrichous ciliate Stylonychia lemnae.

Abstract

A repetitive element from the hypotrichous ciliate Stylonychia lemnae was characterized by restriction and hybridization analysis. This repetitive element is present in about 5,000-7,000 copies per haploid genome in the micronucleus and the macronuclear anlagen. Its DNA sequence is very conserved, but the length of the repetitive sequence blocs is variable. In some cases, it is associated with telomeric sequences and macronucleus-homologous sequences. Restriction analysis of genomic micronuclear and macronuclear anlagen DNA and in situ hybridization showed that the repetitive sequences are amplified during the formation of polytene chromosomes. They are localized in many bands of the polytene chromosomes and are eliminated during the degradation of the polytene chromosomes. Possible functions of the repetitive sequences during macronuclear differentiation are discussed.