SARD, A NEW-PROTEIN ISOLATED FROM THE EXTREMOPHILE ARCHAEON SULFOLOBUS-ACIDOCALDARIUS, IS A THERMOSTABLE RIBONUCLEASE WITH DNA-BINDING PROPERTIES

We have isolated the thermostable 9 kDa SaRD-protein from Sulfolobus a cidocaldarius which exhibits RNase activity as well as DNA-binding pro perties (SaRD). The amino acid composition and the sequence of the 16 N-terminal amino acids show similarities to different RNases as well a s to DNA-binding proteins from thermophilic archea. The RNase activity was demonstrated by 5S rRNA degradation, thin layer chromatography an d a zymogram. The temperature optimum for the RNase activity is 65 deg rees C. The pH optimum ranges from 6.5-7.0. DNA-binding properties wer e shown by gel-shift assays on agarose gels. In a similar way SaRD med iated protection of DNA against DNase I digestion and Sau3A I restrict ion could be demonstrated. The melting point (T-m) of genomic DNA was raised from 68 degrees C to 90 degrees C by addition of the SaRD-prote in. CD spectroscopy indicated that SaRD is very stable near neutral pH and can neither be unfolded by temperatures up to 85 degrees C nor by addition of 8 M urea. (C) 1995 Academic Press, Inc.