Abd1

Abd1 is a gene encoding the N7-methyltransferase responsible for creating the 7-methylguanosine cap at the 5' end of eukaryotic mRNAs, the mRNA cap. In the budding yeast Saccharomyces cerevisiae, Abd1 functions as part of the canonical mRNA capping machinery.

In yeast, Abd1 acts downstream of Cet1, a triphosphatase, and Ceg1, a guanylyltransferase, to form the mature cap 0 structure, m7GpppN. Abd1 transfers a methyl group from S-adenosylmethionine to the N7 position of the added guanine, completing the cap formation process.

The mRNA cap is recognized by cap-binding proteins and plays a key role in mRNA stability, nuclear export, splicing, and efficient translation. Abd1 activity is closely associated with transcription by RNA polymerase II and the carboxy-terminal domain (CTD), supporting transcription-coupled capping of nascent transcripts.

ABD1 is essential for viability in yeast; loss or impairment of Abd1 activity reduces cap methylation, leading to defects in RNA processing and accelerated mRNA decay. Mutants exhibit defects in gene expression at multiple levels due to compromised cap formation.

Orthologs of Abd1 exist across eukaryotes, including humans where the functional counterpart is RNMT, often with regulatory partners such as RAM that modulate activity. While the basic catalytic function is conserved, regulatory context and interacting proteins differ among species.

In research, Abd1 is studied to understand the biology of transcription-coupled mRNA capping and the molecular basis of cap-dependent gene expression. Biochemical and structural studies highlight conserved motifs of S-adenosylmethionine-dependent methyltransferases that underlie Abd1’s catalytic mechanism.

See also: mRNA capping, RNMT, Cet1, Ceg1.