ANALYSIS OF A RIBOSOMAL DNA INTERGENIC SPACER REGION FROM THE YELLOW-FEVER MOSQUITO, AEDES-AEGYPTI

We have sequenced the 1.,8 kb intergenic spacer (IGS) region from an A edes aegypti ribosomal DNA repeat and have identified conserved functi onal motifs shared with the related mosquito, Aedes albopictus, Despit e the shorter length and greater homogeneity of the Ae. aegypti IGS re gion, the sequences of two potential RNA polymerase I core promoters a nd closely associated terminator elements were highly conserved, Prime r extension analysis indicated that the predominant transcription init iation site in the Ae. aegypti rDNA repeat unit region lay at or near the A residue at nucleotide position 1003 in the 'upstream' RNA polyme rase I promoter, This observation was supported by the higher sequence identity between the upstream promoters in Ae. aegypti and Ae. albopi ctus, relative to the downstream promoters, In contrast to strong simi larities among proximal regulatory elements, the Ae, aegypti IGS seque nce upstream of the transcription initiation site lacked the ordered a rray of contiguous similar to 200 nucleotide subrepeats previously fou nd in the IGS of Ae. albopictus. In Ae. aegypti, only 4 similar to 50 nucleotide R subrepeats separated by unique sequences, followed by 2 s imilar to 50 nucleotide E subrepeats, occurred upstream of the transcr iption initiation site, Despite their differences in size and sequence , however, the four Ae. aegypti R subrepeats shared an internal struct ural organization that included a conserved core with 'spacer' promote rs and recombinogenic elements similar to those in the longer Ae. albo pictus subrepeats, These observations provide an important basis for f urther characterization of transcription specificity among mosquito RN A polymerase I promoters and associated regulatory elements, and contr ibute towards the eventual use of these elements in transgenic applica tions.