Identification and chromosomal localization of the monkey retrotransposon in Musa sp.

Retroelements are ubiquitous features of eukaryotic genomes, often accounti ng for a substantial fraction of their total DNA content. One major group o f retroelements, which includes the gypsy and copia-like elements, is disti nguished by the presence of long terminal repeats (LTRs). We have identifie d and partially characterized a sequence from banana (Musa acuminata cv. Gr and Nain) which shows significant homology to gypsy-like LTR retroelements from other species. The element, named monkey, shows a high degree of homol ogy to the reverse transcriptase, RNase H and integrase genes of retroeleme nts from plants, fungi and yeast. However, several stop codons are present in the major ORF of this element, suggesting that this copy of monkey, if f unctional, is non-autonomous. Southern analysis indicated that monkey is pr esent in both the A and B genomes of Musa, and that it is found in 200-500 copies per haploid genome in cv. Grand Nain. Chromosomal localization by fl uorescent in-situ hybridization indicates that copies of monkey are concent rated in the nucleolar organizer regions and colocalize with rRNA genes. Ot her copies of monkey appear to be dispersed throughout the genome.