ABSTRACT
The first ABH protein to be discovered was hABHl, which, among the human homologues,
shows the highest degree of sequence similarity to EcAlkB. In the report describing the initial characterization of hABHl, the protein was reported to complement the alkylation-sensitive phenotype of the E. coli alkB mutant, indicating that it possessed an activity similar to EcAlkB.41 However, subsequent studies failed to reproduce this finding and to detect any EcAlkB-like activ ity associated with the recombinant protein.21*34 Moreover, a recent study reported that mABH 1 knock-out mice are defective in placental development and that the mABH 1 protein associates with nuclear euchromatin, where it binds strongly to a protein involved in gene regulation, suggesting that hABHl /mABH 1 is involved in regulating transcription.42 These findings are in contrast to another recent study which indicated that hABHl is a mitochondrial protein, possessing a rela tively weak activity towards m3C lesions in ssDNA and ssRNA 43 The authors of the latter article did not exclude the possibility that hABHl may act on other substrates and, clearly, more studies are required to firmly establish the biological function of this protein.
