Virus reconstitution and the proof of the existence of genomic RNA.

This paper is a historical overview of the work done on the tobacco mosaic virus. The primary finding was that a virus is capable of reassembling itself from its component protein and RNA, and that only the RNA carries the genomic capability of the virus. This was followed by detailed studies of the chemical and biological properties of viral RNA.

A 55-kDa protein isolated from human cells shows DNA glycosylase activity toward 3,N4-ethenocytosine and the G/T mismatch.

Etheno adducts in DNA arise from multiple endogenous and exogenous sources. Of these adducts we have reported that, 1,N6-ethenoadenine (epsilonA) and 3,N4-ethenocytosine (epsilonC) are removed from DNA by two separate DNA glycosylases. We later confirmed these results by using a gene knockout mouse lacking alkylpurine-DNA-N-glycosylase, which excises epsilonA.

An unusual mechanism for the major human apurinic/apyrimidinic (AP) endonuclease involving 5' cleavage of DNA containing a benzene-derived exocyclic adduct in the absence of an AP site.

The major human apurinic/apyrimidinic (AP) endonuclease (class II) is known to cleave DNA 5' adjacent to an AP site, which is probably the most common DNA damage produced hydrolytically or by glycosylase-mediated removal of modified bases. p-Benzoquinone (pBQ), one of the major benzene metabolites, reacts with DNA to form bulky exocyclic adducts. Herein we report that the human AP endonuclease directly catalyzes incision in a defined oligonucleotide containing 3,N4-benzetheno-2'-deoxycytidine (pBQ-dC) without prior generation of an AP site.

All four known cyclic adducts formed in DNA by the vinyl chloride metabolite chloroacetaldehyde are released by a human DNA glycosylase.

We have previously reported that human cells and tissues contain a 1,N6-ethenoadenine (epsilon A) binding protein, which, through glycosylase activity, releases both 3-methyladenine (m3A) and epsilon A from DNA treated with methylating agents or the vinyl chloride metabolite chloroacetaldehyde, respectively. We now find that both the partially purified human epsilon A-binding protein and cell-free extracts containing the cloned human m3A-DNA glycosylase release all four cyclic etheno adducts--namely epsilon A, 3,N4-ethenocytosine (epsilon C), N2,3-ethenoguanine (N2,3-epsilon G), and 1,N2-ethenoguanine (1,N2-epsilon G). Base release was both time and protein concentration dependent.