A genomic clone encoding the Shaker-related potassium channel gene, Kcna4/mKv1.4, was isolated from mice. Its coding region is contained in a single exon, encodes a protein of 654 amino acids, and shares ∼91% nucleotide sequence identity with human KCNA4/hKv.14. We show that 0.8 kb of the 5′ noncoding region (NCR), the entire protein coding region (∼2.0 kb), and all of the known 3′ NCR (∼ 1.1 kb) are contained within a single exon; the remaining 0.5 kb of the 5′ NCR is separated from this exon by a 3.4-kb intron. The sequenced genomic region thus accounts for essentially all of the longest known transcript (4.5 kb), although the precise ends of this transcript have not been defined. The 3′ NCR contains several ATTTA and ATTTG motifs that are thought to destabilize mRNAs, and these are also present in rat, bovine, and human Kcna4/Kv1.4 cDNAs. It also contains three conserved polyadenylation signals, alternate utilization of which could generate mRNAs of differing stabilities. The 5′ NCR of Kcna4/mKv1.4 may also serve to regulate channel expression. This region is ∼85% identical to KCNA4/hKv1.4 and contains eight consensus translation start sites [(G, A)NNATG] that, based on the 5′-3′ scanning model, would lead to a lowering of translational efficiency. The shortest Kcna4/Kv1.4 transcript (2.4 kb) can contain at most 400 bp of NCR and should lack the 3′ ATTTAs and most of the 5′ ATGs; this transcript might therefore exhibit increased stability and translational efficiency. The Kcna4/mKv1.4 channel exhibited biophysical and pharmacological properties indistinguishable from its rat and human homologues. Kcna4/mKv1.4 lies on mouse chromosome 2, near the Fshb locus, and in humans on the proximal half of chromosome 11p14 near human FSHB. Another K+ channel gene, Kcnc1/mKv3.1, lies ∼1.8 cM from the Myod-1 gene on mouse chromosome 7, and in situ hybridization localizes KCNC1/hKv3.1 to the homologous region on human chromosome 11p14.3-p15.2. A third gene, KCNA1/hKv1.1, was mapped to human 12p13.