The subset of mouse B1 (Alu-equivalent) sequences expressed as small processed cytoplasmic transcripts

Area of Science:

• Molecular Biology
• Genetics
• RNA Biology

Background:

• B1 elements are murine short interspersed elements potentially amplified via RNA intermediates.
• B1-homologous RNAs are heterogeneous transcripts with unknown functions.
• B1 elements are transcribed by RNA polymerase III and processed in cellular compartments.

Purpose of the Study:

• To characterize small cytoplasmic B1 transcripts in mouse cells.
• To investigate the sequence, structure, and processing of B1 RNAs.
• To explore the potential functions of conserved B1 transcripts.

Main Methods:

• cDNA cloning and sequencing of B1 transcripts.
• Sequence identity analysis to develop a novel consensus B1 sequence.
• Structural analysis of conserved domains (Alu domain).
• In vitro processing assays using nuclear extracts.
• Expression studies in injected frog oocytes.

Main Results:

• Identified a subset of B1 RNAs with high sequence identity (98%) and a novel consensus.
• Discovered a conserved Alu domain in a subset of B1 RNAs, homologous to a structure in 7SL RNA.
• Demonstrated that 3'-processing occurs in a subset of B1 transcripts both in vitro and in vivo.
• Observed selective cytoplasmic accumulation of processed B1 transcripts.
• Found no Poly-(A) or 3'-oligo-(U) tracts, suggesting they are not transposition intermediates.

Conclusions:

• A specific subset of B1 sequences is expressed as processed, structurally conserved RNA polymerase III transcripts.
• Selective expression of these B1 RNAs is likely regulated at the post-transcriptional levels of processing and cytoplasmic accumulation.
• The conserved structure and cytosolic localization suggest a role for these B1 RNAs in cellular metabolism, distinct from transposition.