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Applied and Environmental Microbiology, May 2002, p. 2278-2284, Vol. 68, No. 5
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.5.2278-2284.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Transcript Levels of the Eukaryotic Translation Initiation Factor 5A Gene Peak at Early G1 Phase of the Cell Cycle in the Dinoflagellate Crypthecodinium cohnii

K. L. Chan, D. New, S. Ghandhi, F. Wong, C. M. C. Lam, and J. T. Y. Wong*

Biology Department, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong Special Administrative Region, People's Republic of China

Received 25 October 2001/ Accepted 26 December 2001

A cDNA encoding a eukaryotic translation initiation factor 5A (eIF-5A) homolog in heterotrophic dinoflagellate Crypthecodinium cohnii (CceIF-5A) was isolated through random sequencing of a cDNA library. The predicted amino acid sequence possesses the 12 strictly conserved amino acids around lysine 52 (equivalent to lysine 50 or 51 in other eukaryotes). A single 1.2-kb band was detected in Northern blot analysis. In synchronized C. cohnii cells, the transcript level peaked at early G1 and decreased dramatically on the entry to S phase. Although this has not been previously reported, studies of budding yeast (Saccharomyces cerevisiae) and certain mammalian cell types suggest a role for eIF-5A in the G1/S transition of the eukaryotic cell cycle. Phylogenetic trees constructed with 26 other published eIF-5A sequences suggest that CceIF-5A, while falling within the eukaryotic branches, forms a lineage separate from those of the plants, animals, and archaebacteria. The posttranslational modification of eIF-5A by a transfer of a 4-aminobutyl moiety from spermidine to conserved lysine 50 or 51, forming amino acid hypusine, is the only demonstrated specific function of polyamines in cell proliferation. It has been suggested that polyamines stimulate population growth of bloom-forming dinoflagellates in the sea. We demonstrate here putrescine-stimulated cell proliferation. Furthermore, ornithine decarboxylase inhibitor D-difluoromethylornithine and the specific hypusination inhibitor N-guanyl-1,7-diaminoheptane exhibited inhibitory effects in two species of dinoflagellates. The possible links of polyamines and saxitoxin synthesis to the arginine cycle are also discussed.

* Corresponding author. Mailing address: Biology Department, Hong Kong University of Science and Technology, Clearwater Bay, Kowloon, Hong Kong SAR, People's Republic of China. Phone: 852-23587343. Fax: 852-23581559. E-mail: Botin{at}Ust.hk.

Applied and Environmental Microbiology, May 2002, p. 2278-2284, Vol. 68, No. 5
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.5.2278-2284.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.





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