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Chromosome structure in man and amphibia-anura, restriction enzymes

Maria Luiza Beçak; Rita dé Cássia Stocco dos Santos; Marta Dias Soares-Scott; Radenka Francisca Batistic; Heitor Costa

Serviço de Genética, Instituto Butantan, Caixa Postal 65, São Paulo, Brasil. Send correspondence to M.L.B.

ABSTRACT

Fixed metaphase chromosomes from human and from polyploid anurans (Odontophrynus americanus, 4n = 44), were treated with MspI, Hpa II, Eco RI, Bgl II, Dra I and Hae III, restriction enzymes, followed by Giemsa staining. MspI (C 4. CGG) and Hae III (GG y CC) produced G-like bands in human chromosomes indicating that the bands are caused by the removal of CG-rich specific DNA classes. However, comparable G-band patterns were also obtained in human chromosomes with Eco RI (G 4. AATTC), Bgl II (A 4- GATCT) and Dra I (TTT 4. AAA), whose digesting sites do not reveal a particular CG-richness. In the 4n anurans, Mspl removed chromosomal DNA from the long arm of two to three homologues of group I (lq), from the secondary constriction of group 11 as well as from centromeric, telomeric and intercalary C bands. These C bands were not removed ^-with Hpa II (C 4. C:GG), which does not cut methylated DNA. Eco RI caused bands on 2p and 3q. The results suggest that: 1. the action of these enzymes depends on the accessibility of the enzymes to chromosome regions of different DNA packaging. 2. The difficulty in obtaining interstitial bands in anurans may result from the smaller amount of CG-rich sequences probably arranged in small clusters or from the higher level of chromatin packaging in the chromomeres.

Keywords: chromosome; man; amphibia-anura; restriction; enzymes.

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