The Chinese hamster Alu-equivalent sequence: a conserved highly repetitious, interspersed deoxyribonucleic acid sequence in mammals has a structure suggestive of a transposable element.

A consensus sequence has been determined for a major interspersed deoxyribonucleic acid repeat in the genome of Chinese hamster ovary cells (CHO cells). This sequence is extensively homologous to (i) the human Alu sequence (P. L. Deininger et al., J. Mol. Biol., in press), (ii) the mouse B1 interspersed repetitious sequence (Krayev et al., Nucleic Acids Res. 8:1201-1215, 1980) (iii) an interspersed repetitious sequence from African green monkey deoxyribonucleic acid (Dhruva et al., Proc. Natl. Acad. Sci. U.S.A. 77:4514-4518, 1980) and (iv) the CHO and mouse 4.5S ribonucleic acid (this report; F. Harada and N. Kato, Nucleic Acids Res. 8:1273-1285, 1980). Because the CHO consensus sequence shows significant homology to the human Alu sequence it is termed the CHO Alu-equivalent sequence. A conserved structure surrounding CHO Alu-equivalent family members can be recognized. It is similar to that surrounding the human Alu and the mouse B1 sequences, and is represented as follows: direct repeat-CHO-Alu-A-rich sequence-direct repeat. A composite interspersed repetitious sequence has been identified. Its structure is represented as follows: direct repeat-residue 47 to 107 of CHO-Alu-non-Alu repetitious sequence-A-rich sequence-direct repeat. Because the Alu flanking sequences resemble those that flank known transposable elements, we think it likely that the Alu sequence dispersed throughout the mammalian genome by transposition.

Ubiquitous, interspersed repeated sequences in mammalian genomes.

DNA base sequence comparisons demonstrate that the principal family of 300-nucleotide interspersed human DNA sequences, the repetitive double-strand regions of HeLa cell heterogeneous nuclear RNA, and specific RNA polymerase III in vitro transcripts of cloned human DNA sequences are all representatives of a closely related family of sequences. A segment of approximately 30 residues of these sequences is highly conserved in mammalian evolution because it is also present in the interspersed repeated DNA sequences of Chinese hamsters. Further DNA sequence comparisons demonstrate that a portion of this highly conserved segment of repetitive mamalian DNA sequence is similar to a sequence found within a low molecular weight RNA that hydrogen-bonds to poly(A)-terminated RNA molecules of Chinese hamsters and a sequence that forms half of a perfect inverted repeat near the origin of DNA replication in papovaviruses.

Proteolytic enzymes of the K-1 strain of Streptomyces griseus obtained from a commercial preparation (Pronase). Purification and characterization of the carboxypeptidase.

We described earlier the facilitated purifications of the trypsin and aminopeptidase components present in Pronase (Vosbeck, K. D., Chow, K. -F., and Awad, W. M., Jr. (1973) J. Biol. Chem. 248, 6029-6034). A partially resolved protein mixture left over after one of the steps in that procedure was passed through a Sephadex G-75 column. By this means, a component with carboxypeptidase activity was separated from associated serine endopeptidases. Further purification of this exopeptidase to apparent homogeneity was acheived by refiltration through the same Sephadex column and by CM-cellulose chromatography. A single protein band was observed after acrylamide gel electrophoresis; analysis by sedimentation equilibrium using the meniscus depletion method gave a molecular weight of 30,300. This enzyme demonstrates activity against Nalpha-benzyloxycarbonylglycyl-L-leucine and hippuryl-D,L-phenyllactate; no activity was found against Nalpha-acetyl-L-tyrosine ethyl ester, Nalpha-benzoyl-D,L-arginine-p-nitroanilide, or L-leuckne-p-nitroanilide. The maximum activity lies between pH values of 7 and 8; the enzyme is stable between pH values of 6 and 10. At room temperature 1,10-phenanthroline inactivates the enzyme completely whereas EDTA has no effect. Of the many cations tested, only Co2+, Ni2+, or Zn2+ restores activity to the 1,10-phenanthroline-treated enzyme; Co2+ provided 3 times the native activity. The metal in the native protein was found to be zinc. These findings are similar to those recorded with bovine pancreatic carboxypeptidase A, and suggest the possibility that the present enzyme may ge genetically related to the mammalian protein, as in previously noted examples of homology of three Pronase endopeptidases to pancreatic serine enzymes.

Self purification of two serine endopeptidases.

We have reported that a serine protease from Pronase, homologous with bovine chymotrypsin, is both active and stable in 6 M guanidinium chloride. The present investigation examined the possibility that this unique property might be used to permit the enzyme to engage in its own purification by cleaving companion proteins to low-molecular-weight products. Analysis with model substrates of the several specific activities that were originally present revealed that only the activity against Nalpha-acetyl-L-tyrosine ethyl ester was demonstrable after incubation for 100 hr in the denaturant. After a moderate loss within the first 24 hr, the remaining activity against this ester was conserved for many days thereafter. Pronase was routinely incubated for 1 week at 22 degrees in 6 M guanidinium chloride at pH 8.0 where the esterases showed maximal activity. Analysis of the products of incubation revealed unexpectedly the presence of two serine proteases that were easily separated. After purification to homogeneity these components proved themselves to be the previously demonstrated subtilisin-like and stable chymotrypsin-like enzymes. The only amino-terminal residue of the chymotrypsin-like enzyme is isoleucine, as it is in the earlier, conventionally purified product. The migration of the single band of this enzyme during acrylamide gel electrophoresis was the same whether purified by the past or present technique. No free amino-terminal group was demonstrable in the subtilisin-like enzyme. This study presents a unique and rapid technique for isolation of these proteases, with the first reported purification to homogeneity of the subtilisin-like component. These enzymes may be useful as probes for local relaxations of conformation in substrate proteins. Furthermore, they may contribute to the preparation of enzyme-free non-protein macromolecules.