AGO1AGO4

AGO1 and AGO4 are members of the Argonaute family of proteins that play essential roles in RNA silencing pathways. In some scientific contexts, the combined term AGO1AGO4 is used to refer collectively to these paralogs when describing their respective functions, evolutionary relationships, or subcellular roles across different organisms.

All Argonaute proteins share a common domain architecture that typically includes a PAZ domain, a MID domain, and a PIWI domain. The PIWI domain is related to RNase H and, in many Argonautes, contributes to slicer or cleavage activity, though the catalytic competence and functional output can vary among paralogs and species.

AGO1 is a central component of the post-transcriptional gene silencing pathway. It binds small RNAs such as microRNAs (miRNAs) and small interfering RNAs (siRNAs) to guide the repression or degradation of target mRNAs, thereby regulating gene expression post-transcriptionally. In many animals and fungi, AGO1-type proteins are predominantly associated with cytoplasmic silencing complexes that act on mRNA transcripts.

AGO4 functions mainly in plants and is associated with transcriptional gene silencing through RNA-directed DNA methylation (RdDM). AGO4 binds 24-nucleotide siRNAs and participates in a silencing pathway that directs DNA methylation at specific genomic loci, often involving interactions with RNA polymerase V transcripts and DNA methyltransferases, leading to stable, heritable repression of transposable elements and other targets.

Differences between AGO1 and AGO4 reflect the specialization of RNA silencing pathways across kingdoms: AGO1 primarily mediates post-transcriptional suppression of gene expression, while AGO4 contributes to transcriptional silencing and epigenetic modification in plant genomes.