Amino Acid Annotation (A3) Format R package rtemis.a3 version 0.5.3 Implements the Amino Acid Annotation (A3) format using 'S7' classes. The A3 format is a structured schema for annotating amino acid sequences with site, region, post-translational modification (PTM), processing event, and variant information. Provides functions to create, read, and write A3 objects, and to import annotations from 'UniProt', 'AlphaFold', 'PDBe', 'ClinVar', and 'Ensembl'. Software Depends: R (>= 4.1.0) Imports: cli, data.table, rtemis.core, S7, utils Suggests: biomaRt, httr, jsonlite, seqinr, testthat (>= 3.0.0) E.D. Gennatas <gennatas@gmail.com> Comprehensive R Archive Network (CRAN) E.D. Gennatas [aut, cre, cph] (ORCID: <https://orcid.org/0000-0001-9280-3609>) GPL (>= 3) 2026-04-28 application/tgz https://CRAN.R-project.org/package=rtemis.a3 doi:10.32614/CRAN.package.rtemis.a3