As found previously with other Bacillus species, spores of B. stearothermophilus and "Thermoactinomyces thalpophilus" contained significant levels'of small, acid-soluble spore proteins (SASP) which were rapidly degraded during spore gerniination and which reacted with antibodies raised against B. megaterium SASP. Genes codin for a B. stearothermophilus ad a "T. thalpophilus" SASP as well as for two B. cereus SASP wire cloned, their nucleotide sequences were determined, and the amino acid sequences of the SASP coded for were compared. Strikingly, all of the amino acid residues previously found to be conserved in this group of SASP both within and between two other Bacillus species (B. megaterium and B. subtilis) were also conserved in the SASP coded for by the B. cereus genes as well as those coded for by the genes from the more distantly related organisms B. stearothermophilus and "T. thalpophilus."'This finding strongly suggests that there is significant selective pressure to conserve SASP primary sequence and thus that these proteins serve some function other than shuply amino acid storage.Ten to twenty percent of the protein of spores of a number of Bacillus species is degraded in the first minutes of spore germination, thus supplying amino acids for both new prote,in synthesis and metabolism (5,22). The proteins degraded in this process are a group of small, acid-soluble spore proteins (SASP) which are synthesized only during sporulation under transcriptional control (22). In B. megaterium three proteins (termed SASP-A, -B, and.-C) make up -85% of the protein degraded, with SASP-A and -C being very similar in primary sequence and SASP-B being more different (22). Studies of this system at the gene level have revealed that in B. megaterium, in addition to the genes encoding SASP-A and -C, there are five other genes which code for SASP which are very similar to SASP-A and -C (5, 8, 9); this multiplicity of SASP genes' has also been found in B. subtilis (2, 3). Strikingly, the amino acid sequences of the proteins coded for by these different SASP genes exhibit a high degree of homology, with -65% of all residues conserved both within and across species (3,5,9). Given this high degree of SASP sequence conservation, we felt that it might be valuable to analyze SASP genes from other sporulating bacteria, including several more distantly related than' are B. megaterium and B. subtilis. Consequently, in this communication we report the cloning and nucleotide sequence of SASP genes from B. cereus, B. stearothermophilus, and "Thermoactinomyces thalpophilus" MATERIALS AND METHODS Organisms used and isolation of DNA. The organisms used were B. cereus T, (originally obtained from H. 0. Halyorson), B. stearothermophilus NGB101 (11), and "T. thalpophilus" HA-O1 (10). Spores of B. stearothermophilus and "T. thalpophilus" were pr-epared and purified as previously described (10, 11). DNA was also isolated and purified from B. cereus and "'T. thalpophilus" as described previ-* Corresponding author. ously (5, 10). DNA from B. s...