The expression of a unique set of proteins following a heat shock is a universally conserved response (1). The sequences of the different heat shock proteins are also highly conserved between species (2). Recent studies have reported that constitutive expression of a human hsp27 gene product in rodent cells confers a thermoresistant phenotype (3). A genomic sequence for a human hsp27 gene has been reported as well as the cDNA sequences for hsp27 from rat and hamster, respectively (4, 5, 6). We report here the sequence of a cDNA Xphage contained in a library derived from polyA RNA isolated from A549 human lung carcinoma cells 4 hrs after a 45 C, 10 min heat shock. The nucleotide sequence consists of 789 nucleotides containing an open reading frame encoding a 205 amino acid protein. The only difference between the predicted hsp27 message sequence and the cDNA sequence is the addition of two cytosine residues at position 578. The presence of the extra cytosine residues was not detectable when sequencing the coding strand due to a compression, but as shown inFigure 1, the noncoding strand clearly shows the presence of the twoextra nucleotides. The two additional cytosine residues causea shift in the reading frame resulting in the addition of 6 amino acids to the 3'end. The predicted amino acid sequence is 81% identical to both the rat and the hamster hsp27 protein (6) andis 100% identical to human hsp27 protein in the first 193 amino acids. Figure 2 is a comparison of the 3'end of the predicted amino acid sequences.