In recent years several studies showed that chromatin is a complex structure much more dynamic than previously believed and special attention has been devoted to how chromatin activity states are achieved, conserved and modified. One major piece of this puzzle is the H3.3 histone variant. Several data has correlated the local enrichment of Histone 3.3 to transcriptionally active chromatin sites in eukaryotes. Its deposition occurs in a replication independent pathway which regulation and specificity are not completely understood.

We identified and sequenced the Rhynchosciara americana Histone 3.3 (RaH3.3) messenger and started the characterization of this gene. The genomic locus could be isolated and sequenced; the gene structure could be elucidated and its chromosomal localization determined, corresponding to the region 4 on chromosome C. Like in other systems this protein is very similar to the canonical histone H3, showing only four amino acids substitutions, and when compared with Drosophila homologue it presents 100% of similarity, containing only one conservative substitution. We are currently attempting to determine the expression profile and the protein distribution of this histone variant during the development of salivary glands of Rhynchosciara americana, specially in the periods of endoreplication. Such study could contribute to elucidate some structural aspects of the polytene chromosomes, as well as generate maps of the transcriptionally active loci in different larval stages of development.

(FAPESP, CNPq)