Table 1.

RefSeq accession numbers and molecule types.

Accession prefixMolecule typeComment
AC_GenomicComplete genomic molecule, usually alternate assembly
NC_GenomicComplete genomic molecule, usually reference assembly
NG_GenomicIncomplete genomic region
NT_GenomicContig or scaffold, clone-based or WGSa
NW_GenomicContig or scaffold, primarily WGSa
NZ_bGenomicComplete genomes and unfinished WGS data
NM_mRNAProtein-coding transcripts (usually curated)
NR_RNANon-protein-coding transcripts
XM_cmRNAPredicted model protein-coding transcript
XR_cRNAPredicted model non-protein-coding transcript
AP_ProteinAnnotated on AC_ alternate assembly
NP_ProteinAssociated with an NM_ or NC_ accession
YP_cProteinAnnotated on genomic molecules without an instantiated
transcript record
XP_cProteinPredicted model, associated with an XM_ accession
WP_ProteinNon-redundant across multiple strains and species
a

Whole Genome Shotgun sequence data.

b

An ordered collection of WGS sequence for a genome.

c

Computed.

From: Chapter 18, The Reference Sequence (RefSeq) Database

Cover of The NCBI Handbook
The NCBI Handbook [Internet].
McEntyre J, Ostell J, editors.
Bethesda (MD): National Center for Biotechnology Information (US); 2002-.

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.