Characterization of human 5S rRNA genes

Area of Science:

• Molecular Biology
• Genetics
• Human Genomics

Background:

• Human 5S ribosomal RNA (rRNA) genes are organized in tandemly repeated units.
• These repeat units form distinct clusters within the genome.

Purpose of the Study:

• To clone and characterize restriction fragments from human 5S rRNA gene clusters.
• To investigate the structural variations and copy number of 5S rRNA genes and their variants.
• To assess the transcriptional regulation of 5S rRNA genes.

Main Methods:

• Gene cloning and partial characterization using restriction fragment analysis.
• Analysis of gene variants and flanking regions.
• In vitro transcription assays using HeLa cell extracts.

Main Results:

• Identified 2.3 kb and 1.6 kb repeat clusters containing 5S rRNA genes and a gene variant.
• Characterized a gene variant with an internal control region alteration and a 1.6 kb repeat with a 3'-flanking deletion.
• Estimated 300-400 5S rRNA genes/variants and 1700-2000 total 5S rRNA sequences per haploid genome.
• Demonstrated equal transcription of genes and variants, with significant reduction upon removal of upstream 5'-flanking sequences.

Conclusions:

• Human 5S rRNA genes are present in multiple copies within different repeat clusters.
• Upstream regulatory sequences, particularly a GC-motif, are critical for efficient 5S rRNA gene transcription.