The human histone H2A.Z gene. Sequence and regulation

Area of Science:

• Molecular Biology
• Genetics
• Epigenetics

Background:

• The H2A.Z gene encodes a basal histone variant crucial for chromatin structure.
• Understanding H2A.Z gene regulation is vital for comprehending cellular processes like proliferation and quiescence.

Purpose of the Study:

• To clone and sequence the human H2A.Z gene.
• To investigate the transcriptional regulation of H2A.Z.
• To compare the human H2A.Z gene organization with its chicken ortholog.

Main Methods:

• Gene cloning and sequencing.
• Analysis of upstream and downstream DNA sequences.
• Measurement of H2A.Z transcript levels in proliferating and quiescent cells.
• Chloramphenicol acetyltransferase (CAT) reporter gene assays to delineate promoter activity in IMR-90 cells.

Main Results:

• A single functional human H2A.Z gene was identified, along with pseudogenes. No other histone genes were found in flanking regions.
• H2A.Z transcript levels are independent of DNA replication but decrease significantly as cells become quiescent, linked to reduced transcription rates.
• Maximal promoter activity was localized to a 234-base pair region upstream of the transcription start site, containing GC boxes, CCAAT boxes, and a TATA box.
• The human H2A.Z gene shares structural similarities with the chicken H2A.Z gene, including identical exon-intron borders, though intron lengths differ. Promoter regions show limited homology, with conserved GC and CCAAT boxes.

Conclusions:

• The human H2A.Z gene structure is conserved across species.
• Transcriptional regulation, particularly the decrease in transcription rate, plays a key role in modulating H2A.Z levels during cellular quiescence.
• The identified promoter elements are critical for H2A.Z gene expression.