No abstract

The antarctic fish Notothenia coriiceps neglecta synthesizes eight antifreeze glycopeptides (AFGP 1-8; Mr 2600-34,000) to avoid freezing in its ice-laden freezing habitat. We report here the sequence of one of its AFGP genes. The structural gene contains 46 tandemly repeated segments, each encoding one AFGP peptide plus a 3-amino acid spacer. Most of the repeats (44/46) code for peptides of AFGP 8; the remaining 2 code for peptides of AFGP 7. At least 2 of the 3 amino acids in the spacers could act as substrate for chymotrypsin-like proteases. The nucleotide sequence between the translation initiation codon (ATG) and the first AFGP-coding segment is G + T-rich and encodes a presumptive 37-residue signal peptide of unusual sequence. Primer extension establishes the transcription start site at nucleotide 43 upstream from ATG. CAAT and TATA boxes begin at nucleotides 53 and 49, respectively, upstream from the transcription start site. The polyadenylylation signal, AATAAA, is located approximately 240 nucleotides downstream from the termination codon. A mRNA (approximately 3 kilobases) was found that matches the size of this AFGP gene. Thus, this AFGP gene encodes a secreted, high-copy-number polyprotein that is processed posttranslationally to produce active AFGPs.

A nuclear genomic library of Glycine max generated in Charon 35 was a gift from Dr R. Nagao. A 2.3 kbp long HindIII fragment (AB2.3) was cloned in the high copy plasmid pTZ-19R and the 5' 911 nucleotides were dideoxy-sequenced (Fig. 1). Nucleotides 1 -4 4 code a portion of a transit peptide. Homology block III [3] is located at nucleotides 21-44 and is preceded by a less homologous "interblock" at nucleotides 3 -20. An open reading frame from methionine at nucleotide 45 to a TGA termination codon (nucleotides 738-740) codes a mature LHCPII when the deduced amino acid composition is compared to published LHCPII proteins. The mature LHCPII has a calculated molecular weight of 28 891. The DNA and deduced amino acid sequences are highly homologous with those of other higher plants, e.g., 84°7o and 93%, respectively, with pea AB80 [1]. The amino acid sequence of the transit peptide and the amino-terminus of the mature protein indicates that AB2.3 is a class 1 LHCPII [4].