We have sequenced a second gene of the hsp70 family derived from a genomic clone of the sea urchin, Paracentrotus lividus. The structure of this gene, named hsp70IV gene, is interrupted by one intron and differs from the previously analyzed sea urchin hsp70II gene, which contains several introns. Two open reading frames of hsp70IV gene encode a predicted protein of 639 amino acids with an M(r) of 69,672. The 5' flanking region of the gene contains a putative TATA element, three heat-shock elements made up of some arrays of the 5-bp units, NGAAN and NTTCN (N = A,C,G or T), a canonic consensus sequence for binding of the regulatory activating transcription factor (ATF), and a purine box. The 3' flanking region contains four putative polyadenylation sites located at different sites downstream from the stop codon. Using Northern blot hybridization analysis, carried out using a probe corresponding to a 3' noncoding fragment (UTR) peculiar to hsp70IV gene, we found that this gene is transcribed only under heat shock (Hs) and that the transcript can be recovered from the polysomal pellet. The hsp70IV gene may be classified as a Hs gene 70 although it contains one intron.