Protein isoform

A protein isoform is one of multiple protein forms associated with a gene, differing in amino-acid sequence or processing. Isoforms can have distinct properties, locations, or functions.

Alternative splicing: A process that joins different combinations of exons from one pre-mRNA to produce distinct RNA molecules. It changes which coding segments contribute to a protein isoform.
Gene: A DNA sequence that contributes to a functional product, such as an RNA or protein. A gene is the shared source from which its protein isoforms arise.
Tropomyosin: A family of actin-binding proteins that regulate actin filaments in muscle and nonmuscle cells. Its many isoforms show how tissue-specific forms can support distinct cellular roles.
Allelic variant: A version of a gene sequence that differs among individuals or chromosomes. Allelic variants arise from DNA differences, unlike many isoforms produced from one gene.
Alternative promoters: Distinct promoters that initiate transcription at different positions within a gene. Different start sites can produce proteins with different N-terminal regions.
Exon: A segment retained in a mature RNA after introns are removed. Alternative inclusion of exons often accounts for sequence differences between isoforms.
BCL2L1: A gene encoding Bcl-x protein forms that can either promote or inhibit apoptosis. Its alternative splicing produces forms with opposing effects on cell survival.
Protein isoform (genetic variant): A protein form encoded by a distinct allele of a gene. Some usage calls allele-derived proteins isoforms, though the term often emphasizes processing differences.
Alternative polyadenylation: The use of different polyadenylation sites to create RNA transcripts with different 3′ ends. Some transcripts acquire or lose coding sequence, changing the resulting protein.
Intron: A segment of a gene transcribed into RNA but usually removed during RNA splicing. Introns provide boundaries where alternative splice choices can be made.

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ProteomeBroader topic: Distinct isoforms can expand the protein forms counted in a proteome.