Utilization of exogenous thymidine by Chlamydia psittaci growing in the thymidine kinase-containing and thymidine kinase-deficient L cells

Abstract

The incorporation of [3H]thymidine into the deoxyribonucleic acid (DNA) of Chlamydia psittaci (strain 6BC) growing in thymidine kinase (adenosine 5'-triphosphate-thymidine 5'-phosphotransferase, EC 2.7.1.21)-containing L cells, L(TK+), and thymidine kinase-deficient L cells, LM(TK-), was examined by autoradiography. Label was detected over C. psittaci inclusions in L(TK+) but not LM(TK-) cells. No evidence for a chlamydia-specific thymidine kinase activity in either L(TK+) or LM(TK-) cells was obtained. Entry of [3H]thymidine into the DNA of C. psittaci growing in L(TK+) cells was quantitated by measuring label in purified C. psittaci. It was 265 times less efficient than entry into infected host cell DNA. It is concluded that low levels of exogenous thymidine are incorporated into the DNA of C. psittaci and that this incorporation is dependent on a fully competent host thymidine kinase activity. Evidence also is presented that L cells possess at least two thymidine kinase activities, both of which are capable of supplying thymidylate precursors for nuclear DNA synthesis.

Diversity in nucleotide acquisition by antigenically similarChlamydia psittaciof avian origin

“…In keeping with results obtained with C. psittaci Cal-10 [10] and C. trachomatis L2 [13], C. psittaci 6BC readily incorporated exogenously supplied adenine, guanine, cytidine and uridine into chlamydial specific DNA (Table 1). Also in agreement with earlier studies [7] we found that exogenous thymidine was not utilized by C. psittaci 6BC. Unexpectedly, we obtained a very different pattern of precursor utilization with the C. psittaci strain francis isolate AA Mp.…”

“…It has been generally accepted that, in contrast to ribonucleotides, chlamydiae are unable to salvage deoxyribonucleotides or deoxyribonucleosides from the host cell [7,13]. Since we now find that the unusual C. psittaci isolates can efficiently utilize exogenous thymidine we have to modify this generalization.…”

“…Over the years, work on nucleotide metabolism in C. psittaci strains 6BC [7][8][9] and francis Cal-10 [10], and in C. trachomatis strain L2 [11][12][13][14][15] have arrived at similar conclusions. At the present time all evidence indicates that as a genus Chlamydia (a) are auxotrophic for all four ribonucleoside triphosphates (NTPs); (b) cannot salvage purine or pyrimidine bases or (deoxy)nucleosides; (c) can obtain all four NTPs from the host, by as yet unidentified transport system(s); and (d) cannot transport host-supplied deoxyribonucleoside triphosphates (dNTPs).…”

Comparative biology of intracellular parasitism.

“…Chlamydiae readily incorporate most medium-supplied nucleosides into DNA and RNA, but the pyrimidine deoxyribonucleosides are utilized very poorly (416). C. psittaci has no detectable thymidine kinase of its own, and it grows normally in thymidine kinase-deficient L cells (177,247). Chlamydiae probably make the most of the thymidine tnphosphate needed for DNA synthesis from uridine via thymidylate synthetase.…”

“…Competition has been most studied in C. psittaci and L cells. Chlamydiae and host cells sometimes compete on an even footing, as when C. psittaci incorporates uridine into its rRNA at a rate consistent with free access to the ribonucleoside triphosphate pools of the L cell (175), but it completes poorly with the L cell for thymidine (177). Only in the presence of exceptionally high external levels of the nucleoside, and with the host cell synthesizing the deoxyribonucleoside phosphates of thymine, do the chlamydiae incorporate even traces of thymidine into their DNA.…”