Ribonuclease H(70) from Saccharomyces cerevisiae possesses cryptic reverse transcriptase activity.

Area of Science:

• Molecular Biology
• Yeast Genetics
• Enzymology

Background:

• Yeast cells harbor proteins with enzymatic activities relevant to retroviral replication.
• RNase H and reverse transcriptase activities are crucial for retroviral pol gene function.
• Retroviral elements like Ty elements and mitochondrial introns are found in yeast.

Purpose of the Study:

• To characterize a yeast protein exhibiting both RNase H and reverse transcriptase activities.
• To investigate the relationship of this protein to known retroviral gene products and yeast retrotransposons.
• To determine the potential origin of the identified dual-activity protein.

Main Methods:

• Purification and characterization of a 70 kDa yeast protein.
• Assay of RNase H and reverse transcriptase activities.
• Immunological analysis using polyclonal antibodies against the 70 kDa protein.
• Comparison of protein properties with known retroviral pol gene products.

Main Results:

• A 70 kDa yeast protein with RNase H activity was identified.
• This protein and related 160 kDa proteins from yeast extracts share reverse transcriptase activity.
• These proteins resemble products of retroviral pol genes.
• Experimental data suggest the protein is not encoded by known retrotransposon family elements.

Conclusions:

• Yeast possesses a unique protein combining RNase H and reverse transcriptase functions.
• This protein is immunologically related to other yeast proteins with similar enzymatic activities.
• The findings suggest a potential cellular origin for this dual-activity enzyme, possibly from a gene distantly related to retrotransposons.