Characterization and purification of flap endonuclease-1 (xiFEN-1) from Xiphophorus maculatus

Gene cloning and characterization of Tk1281, a flap endonuclease 1 from Thermococcus kodakarensis

Flap endonuclease is a structure-specific nuclease which cleaves 5'-flap of bifurcated DNA substrates. Genome sequence of Thermococcus kodakarensis harbors an open reading frame, Tk1281, exhibiting high homology with archaeal flap endonucleases 1. The corresponding gene was cloned and expressed in Escherichia coli, and the gene product was purified to apparent homogeneity. Tk1281 was a monomer of 38 kDa and catalyzed the cleavage of 5'-flap from double-stranded DNA substrate containing single-stranded DNA flap. The highest cleavage activity was observed at 80 °C and pH 7.5. Under optimal conditions, Tk1281 exhibited apparent V_max and K_m values of 278 nmol/min/mg and 37 μM, respectively, against a 54-nucleotide double-stranded substrate containing a single-stranded 5'-flap of 27 nucleotides. A unique feature of Tk1281 is its highest activation in the presence of Co²⁺ and no activation with Mn²⁺. To the best of our knowledge, this is the first cloning and characterization of a flap endonuclease from the genus Thermococcus.

Perturbation of DNA repair gene expression due to interspecies hybridization

The effect of interspecies hybridization on gene regulation was examined using real-time polymerase chain reaction (RT-PCR) to measure the expression of five base-excision repair genes in brain, eye, gill, liver, and tailfin tissues from Xiphophorus parental species and F(1) hybrids. Relative mRNA levels of uracil N-glycosylase (Ung), Apurinic/apyrimidinic endonuclease (Ape1), polymerase-beta (Polb), flap endonuclease (Fen1), and DNA ligase (Lig1) were measured in three parental Xiphophorus species (X. maculatus Jp 163 B, X. helleri Sarabia, and X. andersi andC) and in two interspecies F(1) hybrids, the Sp-helleri hybrid (X. maculatus Jp 163 BxX. helleri Sarabia) and the Sp-andersi hybrid (X. maculatus Jp 163 BxX. andersi) to identify genes that undergo changes in expression levels upon interspecies hybridization. Significant differences in gene expression were observed between parental animals and their respective F(1) hybrids in both interspecies crosses. Generally, marked increases in DNA repair gene mRNA levels were observed across all tissues in F(1) hybrid animals from the Sp-helleri cross compared to either X. maculatus or X. helleri parents. In contrast, the Sp-andersi F(1) hybrid animals generally exhibited decreased base-excision repair gene expression, although this trend was more specific to individual tissues than observed for Sp-helleri hybrids.