The ultraviolet circular dichroism spectra of human lysozyme are presented. Effects of pH and added inhibitor (N-acetyl-D-glucosamine) were examined and the results were compared with similar measurements of hen egg-white lysozyme. The near-ultraviolet CD spectral bands are substantially different in the human and hen egg-white enzymes. In addition to marked dissimilarities in the spectral interval 260-300 nm, an unusual CD band occurs at an anomalous wavelength (313 nm) in human lysozyme. The pH dependence of the latter suggests a possible interaction, absent in hen egg-white lysozyme, between a tryptophan and a tyrosine residue. Analysis of the spectra furthermore suggests lesser net rotational strengths of tryptophan bands in hen egg-white lysozyme than in human lysozyme, although the latter has one less tryptophan residue. The relationship between the CD spectra and the sequence differences of the proteins is discussed, as well as the CD spectra (published by others) of a closely related protein, bovine alpha-lactalbumin. Contributions of cystine residues to the spectra are examined in the light of possible differences in chirality of one of the four disulfide bridges.The far-ultraviolet CD spectra of human and egg-white lysozyme are quite similar, though not identical. In view of the pronounced differences in side-chain optical activity, and of the effect of pH variation on the far-ultraviolet CD spectrum of human lysozyme, it is likely that at least part of the observed difference in spectra is due to nonpeptide optical activity, and that the proteins have a secondary structure in common.

Amino Acid Sequence↗

PubMed1971

Repair of alkylated bacteriophage T4 deoxyribonucleic acid by a mechanism involving polynucleotide ligase.

Methyl methanesulfate-induced lesions in bacteriophage T4 are repaired primarily by a mechanism involving polynucleotide ligase. Apparently, other recombinational and ultraviolet repair functions aren't involved.

Adsorption↗

PubMed1971

Reversion of frameshift mutations stimulated by lesions in early function genes of bacteriophage T4.

Temperature-sensitive (ts) mutants representative of a number of genes of phage T4 were crossed with rII mutants to allow isolation of ts, rII double-mutant recombinants. The rII mutations used were characterized as frameshift mutations primarily on the basis of their revertability by proflavine. For each ts, rII double mutant, the effect of the ts mutation on spontaneous reversion of the rII mutation was determined over a range of incubation temperatures. A strong enhancement in reversion of two different rII mutants was detected when they were combined with tsL56, a mutation in gene 43 [deoxyribonucleic acid (DNA) polymerase]. Three other mutants defective in gene 43 enhanced reversion about fourfold. Two mutations in gene 32, which specifies a protein necessary for DNA replication, enhanced reversion about 5-fold and 18-fold, respectively. Two additional mutations in gene 43 and two in gene 32 had no effect. Fivefold and threefold enhancements in reversion were also found with mutations in genes 44 (DNA synthesis) and 47 (deoxyribonuclease), respectively. No significant effect was found with mutations in seven additional genes. The results of other workers suggest that frameshift mutations arise from errors in strand alignment during repair synthesis occurring at chromosome tips. Our results show that such errors can be enhanced by mutations in the DNA polymerase, the gene 32 protein, and the enzymes specified by genes 44 and 47. This implies that these proteins are employed in the repair process occurring at chromosome tips and that mutational errors in these proteins can lead to loss of ability to recognize and reject strand misalignments.

Adenine↗

PubMed1970