Functional elements residing within satellite DNAs

Abstract

Satellite DNAs represent a fast-evolving portion of the eukaryotic genome whose evolution is proposed to be driven by the stochastic process of molecular drive. Recent results indicate that satellite DNAs are subject to certain structural constraints, which are probably related to their interaction with proteins involved in the establishment of specific chromatin structures. The evolutionary persistence and high sequence conservation of some satellites, as well as the presence of stage- or tissue-specific, differentially expressed transcripts in several species, are consistent with the hypothesis that satellite DNA could have a regulatory role in eukaryotic organisms. Although the role of most transcripts is not known, some act as precursors of small interfering RNAs, which are now recognized as having an important role in chromatin modulation and the control of gene expression. Furthermore, some transcripts are involved in the cellular response to stress.

Figure 1

Schematic representation of a satellite monomer and the processes in which satellite DNAs are involved. Common functional elements such as periodically distributed AT tracts, centromere protein B (CENP-B) box and a promoter are indicated. A superhelical structure induced by DNA curvature, together with chromatin proteins such as CENP-B, could contribute to heterochromatin formation. Transcription of satellite DNAs proceeds either in the form of double-stranded RNA (dsRNA) or single-stranded RNA (ssRNA). dsRNA is processed into small interfering RNAs (siRNAs) that participate in heterochromatin formation and control expression of sequences tagged with complementary repeats. Single-stranded transcripts with hammerhead-like secondary structure have self-cleavage activity and function as ribozymes. Some ssRNAs, such as human satellite III stress-induced transcripts, specifically recruit splicing factors to nuclear stress granules and regulate splicing.