Genetic Engineering Manual Advanced Bacterial Genetics: A Manual for Genetic Engineering R. W. Davis D. Botstein J. R. Roth

Abstract— An ammonium‐sulfate‐precipitable (33–70%) fraction in extracts from eggs of silkworm Bombyx mori contains photoreactivating enzyme that reactivates the transforming activity of UV inactivated Hemophilus influenzae DNA. The action spectrum for in vitro photoreactivation with the enzyme has a broad peak around 365–385 nm, with a shoulder extending to 460 nm. This relatively higher photoreactivation efficiency at wavelengths longer than 450 nm seems to be a unique feature of DNA photoreactivating enzyme of silkworm. Using gel filtration, a mol wt of 42,000 was estimated for the enzyme. Optimum and isoionic pH of the enzyme were 7.2 and 5.4, respectively. These properties of silkworm enzyme are within the range of variations in reported biochemical characteristics of photoreactivating enzymes from different species.

Section: Introductionmentioning

confidence: 99%

Dna Photoreactivating Enzyme From Silkworm

Muraoka

Okuda

Ikenaga

1980

“…similar to those used here. the fraction of potential sites actually dimerized is much greater for thymine dimers than for the otheitwo types (Setlow and Carrier. 1966;Unrau et u/.. 1973).…”

Section: Resultsmentioning

confidence: 99%

Blockage of Restriction Endonuclease Cleavage by Thymine Dimers

Hall¹,

Larcom²

1982

Viral DNAs were subjected to 254 nm irradiation and then digested with type II restriction endonucleases. At the fluences used, irradiation inhibited cleavage by nucleases which recognize sites containing neighboring thymines. Cleavage by endonucleases with other recognition sequences was not affected. In viral and plasmid DNAs, this effect could be used to study thymine dimer formation at a few specific, mapped sites of defined base sequence.

“…The relatively small difference between the recalculated P D unwinding angles could also be interpreted in terms of difference in base composition of the dimer itself. UV radiation <300 nm generates dimers containing both thymine and cytosine (Setlow and Carrier, 1966). while irradiation of DNA complexed with silver generates dimers to which cytosine-containing dimers contribute less than 3% (Kahn.…”

Section: Disc~ssionmentioning

confidence: 99%

IRRADIATION OF CIRCULAR DNA WITH 254 nm RADIATION OR SENSITIZATION IN THE PRESENCE OF Ag+ EVIDENCE FOR UNWINDING BY PHOTOPRODUCTS OTHER THAN PYRIMIDINE DIMERS

Ciarrocchi

Sutherland

1983

Abstract— Structural alterations of DNA irradiated with UV light were analyzed by the agarose gel technique. Relaxed, circular pAT 153 DNA molecules were sensitized by broad band radiation with a maximum at 313 nm in the presence of silver ions or irradiated with 254 nm light in buffer only. In both cases the electrophoretic mobility of DNA topoisomers was altered as a linear function of UV exposure. For DNA irradiated in the sensitized reaction the unwinding angle per site sensitive to Micrococcus luteus pyrimidine dimer endonuclease was found tobe–11.4°. This value is significantly smaller thanthe–14.3° already known for DNA topoisomers irradiated with 254 nm light. The irradiated DNAs were a very good substrate for the Escherichia coli photoreactivating enzyme (PRE). However, the photoenzymic removal of all sites sensitive to the endonuclease specific for pyrimidine dimers was not coupled to a full restoration of the original electrophoretic mobility. Thirty and 23% of the unwinding were still present in the photoreactivated topoisomers and the unwinding angles per pyrimidine dimer were then recalculatedas–10.1°and–8.7° for DNAs irradiated with 254 nm and sensitized, respectively. The limited difference between these two values could result from the different base composition of the pyrimidine dimers generated in the conditions of irradiation used. These results show that the tertiary structure of DNA is measureably altered by UV photodamages other than pyrimidine dimers.