Abstract: In accordance with the present invention, there are provided selection systems and methods for screening for agents that control splicing of inteins in their native host protein (extein) or in homologous exteins. Specifically, there are provided positive genetic selection systems for the screening of agents which inhibit or activate protein splicing which comprise: a host cell containing a chromosomal gene encoding either a drug-resistant form of a target enzyme or a wild-type target enzyme, and a plasmid-borne gene encoding either a drug-sensitive form of the target enzyme, which is dominantly cytotoxic upon interaction with the drug, or a dominantly cytotoxic form of the target enzyme. In these systems the plasmid-borne gene contains an intein, and the inhibition or activation of splicing of the dominant cytotoxic form of the target enzyme by a given reagent results in the survival or death of the host cell. More specifically, positive genetic selection systems that utilize the M. xenopi GyrA intein or M.

Abstract: Recombinant DNA polymerases from archaebacteria as well as isolated DNA coding for such polymerases are provided. The isolated DNA is obtained by use or DNA or antibody probes prepared from the DNA encoding T. litoralis DNA polymerase and the T. litoralis DNA polymerase respectively. Also provided are methods for producing recombinant archaebacteria thermostable DNA polymerase and methods for enhancing the expression of such polymerases by identifying, locating and removing introns from within the DNA coding for such DNA polymerases.

Abstract: Recombinant DNA polymerases from archaebacteria as well as isolated DNA coding for such polymerases are provided. The isolated DNA is obtained by use of DNA or antibody probes prepared from the DNA encoding T. litoralis DNA polymerase and the T. litoralis DNA polymerase respectively. Also provided are methods for producing recombinant archaebacteria thermostable DNA polymerase and methods for enhancing the expression of such polymerases by identifying, locating and removing introns from within the DNA coding for such DNA polymerases.

Abstract: Recombinant DNA polymeraset from archaebacteria as well as isolated DNA coding for such polymeraset are provided. The isolated DNA is obtained by use of DNA or antibody probet prepared from the DNA encoding T. litoralis DNA polymerate and the T. litoralis DNA polymerate respectively. Also provided are meshocs for producing recombinant archaebacteria thermostable DNA polymerase and methods for enhancing the expression of such polymeraset by identifying, locating and removing introns from within the DNA coding for such DNA polymerases.

Abstract: There is provided an extremely thermostable enzyme obtainable from Thermococcus litoralis. The thermostable enzyme has a molecular weight of about 90,000-95,000 daltons, a half-life of about 60 minutes at 100.degree. C. in the absence of stabilizer, and a half-life of about 95 minutes at 100.degree. C. in the presence of stabilizer, such as octoxynol (TRITON X-100) or bovine serum albumin. The thermostable enzyme possesses a 3'-5' proofreading exonuclease activity. The thermostable enzyme may be native or recombinant and may be used for second-strand cDNA synthesis in cDNA cloning, DNA sequencing, and DNA amplification.