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Cessation of Nuclear DNA Synthesis in Differentiating Naegleria *
Author(s) -
CORFF SONDRA,
YUYAMA SHUHEI
Publication year - 1976
Publication title -
the journal of protozoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 0022-3921
DOI - 10.1111/j.1550-7408.1976.tb03847.x
Subject(s) - dna synthesis , biology , thymidine , dna , nuclear dna , dna replication , cytoplasm , microbiology and biotechnology , cell cycle , naegleria , cell , biochemistry , genetics , protozoa , mitochondrial dna , gene
SYNOPSIS. DNA synthesis during growth and differentiation in Naegleria gruberi strain NEG populations has been studied. Autoradiography of cells labeled with [ 3 H]thymidine revealed that grains are concentrated over the nuclei in logarithmically growing populations of cells, whereas in differentiating cells, grains are scattered over the cytoplasm; i.e. no significant nuclear labeling is detectable. It was established by MAK chromatographic analysis that [ 3 H]thymidine is incorporated into double‐stranded DNA in Naegleria and that the actual amount of incorporation in the logarithmically growing populations of cells is 20 times greater than that in differentiating cells. These results suggest that nuclear DNA synthesis is reduced markedly soon after the initiation of differentiation, while cytoplasmic DNA synthesis continues. It was established from cell cycle analysis that the approximate intervals of G 1 , S, G 2 , and M phases were 180, 183, 90, and 28 min, respectively. Hence, the reduction in the nuclear DNA synthesis in differentiating cells is not due to the inhibition of initiation of DNA replication, but rather to the termination of the DNA replicating process. Thus DNA synthesis is curtailed in the presence of RNA and protein synthesis which are required for differentiation.