Title: Molecular evolution of ribosomal intergenic spacers in Odontophrynus americanus 2n and 4n (Amphibia : Anura)

Author(s):  Alvares LE, Polanco C, Brison O, Coutinho LL , Ruiz IRG

Source:  GENOME 45 (1): 71-81 FEB 2002

Document Type:  Article

Language:  English

Abstract:  Ribosomal intergenic spacers (IGSs) of Odontophrynus americanus 2n and 4n were cloned, restriction mapped, and partially sequenced. Three distinct regions, namely alpha, beta, and delta, were identified in the IGSs. The alpha and beta regions flanked the 28S and 18S rRNA genes, respectively, conserving an identical restriction pattern at each ploidy level. The delta region, located between alpha and beta, was highly variable in size and restriction pattern, enclosing different BamHI subrepeats (B-SR), 87- to 530-bp-long. Sequence analysis showed that B-SRs were composed mainly of different arrangements of similar blocks of sequences. Another family of repetitive sequences was found in the delta region, clustered inside large BamHI fragments. These subrepeats are 189-bp-long and, although very similar in diploid and tetraploid IGSs, show a pattern of concerted evolution. A hypothetical functional role for the 189-bp repeats is discussed in view of their predicted secondary structure and presence of potential E2 binding sites inside diploid subrepeats. Although the same structural elements were present both in diploid and tetraploid IGSs, the higher level of repeatability of tetraploid IGSs suggests that common ancestor sequences have undergone several rounds of amplification after O. americanus polyploidy.

Author Keywords:  Odontophrynus americanus; amphibian polyploidy; ribosomal DNA; intergenic spacer; IGS subrepeats

KeyWords Plus:  MULTIPLE SEQUENCE ALIGNMENT; GENE-TRANSCRIPTION; VIRAL INTEGRATION; REPETITIVE DNA; POLYMERASE-I; E2 PROTEIN; RNA; ORGANIZATION; TRITURUS; XENOPUS

Addresses:  Ruiz IRG (reprint author), Butantan Inst, Genet Lab, Av Vital Brasil 1500, Sao Paulo, BR-05503900 Brazil
Butantan Inst, Genet Lab, Sao Paulo, BR-05503900 Brazil
Univ Sao Paulo, Escola Super Agr Luiz de Quieroz, Biotechnol Lab, Piracicaba, SP Brazil
Univ Leon, Fac Biol, Area Genet, Leon, E-24071 Spain
Inst Gustave Roussy, Oncol Genet Lab, Villejuif, France Publisher:  NATL RESEARCH COUNCIL CANADA, RESEARCH JOURNALS, MONTREAL RD, OTTAWA, ONTARIO K1A 0R6, CANADA

Subject Category:  BIOTECHNOLOGY & APPLIED MICROBIOLOGY; GENETICS & HEREDITY

IDS Number:  516KT

ISSN:  0831-2796