An Unusual Pattern of Tritiated Thymidine Incorporation in Euglena

SYNOPSIS. Thymidine-methyl-H² is incorporated into the cytoplasm of Euglena . The label is non-nuclear and not in DNA; evidence for its presence in RNA and protein is presented. Only Euglena which maintain the potentiality to develop chloroplasts show this incorporation; it was not observed in streptomycin. uv, benadryl, O-methyl threonine or heat "bleached" Euglena , nor in Astasia longa.
Preliminary incorporation experiments show that exogenous pyrimidines are not utilized as nucleic acid precursors in Euglena in general. However, the tritiated purines are incorporated into DNA and RNA. The use of thymidine to localize DNA autoradiographically in Euglena is completely excluded.