| Summary: | Pachycara brachycephalum (suborder Zoarcoidei) produces essentially one antifreeze peptide (AFP) that is maintained at high serum levels. The AFP gene family of the species was characterized to elucidate the basis of its particularly homogeneous AFP complement, as compared with other zoarcoids. Six AFP genes were isolated from a genomic DNA library. Four of the genes are similar in sequence to other zoarcoid AFP genes, encode proteins similar to the predominant AFP (AB1) and are termed "classical" genes. The fifth AFP gene contains a 648-bp insertion with the 3$\sp\prime$ exon (as compared with the "classical" gene motif) and is termed "AFP-like." The sixth AFP gene sequence lacks the "classical" 5$\sp\prime$ exon and nearly identical to a 3$\sp\prime$ region of a partial gene sequence of the antarctic zoarcoid Lycodichthys dearborni that is suspected to encode a multi-domain AFP similar to one of its major AFPs, RD3. This sequence in P. brachycephalum is termed "RD3-like." The AFP gene family of P. brachycephalum contains $\sim$83 genes, of which about 46 are "classical," 24 are "AFP-like" and eight are "RD3-like." While no protein products are known for "AFP-like" and "RD3-like" genes, a cDNA transcript from each was obtained, indicating that each is expressed. Messages for AB1 comprise the majority of the "classical" gene transcripts. Messages for the known minor AFP variant (AB2) and for seven other variants were also identified. The species' essentially monotypic circulating AFP complement is thus encoded by a large gene family, as in other zoarcoids. Few consistencies exist in the AFP genes' flanking regions. Neighboring genes are separated by at least five distances: 0.5, 0.7, 2.0, 10.5, and 11.7 kbp. This irregular AFP gene arrangement is similar to that of the Atlantic ocean pout Zoarces americanus, but is in sharp contrast to the $\sim$8-kbp tandemly repeating AFP gene arrangement in Lycodichthys dearborni and in the more distantly related Atlantic wolffish Anarhichas lupus. This variation in zoarcoid ...
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