Nucleic Acids Research Advance Access originally published online on September 27, 2008
Nucleic Acids Research 2008 36(19):6048-6055; doi:10.1093/nar/gkn596
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Nucleic Acids Research, 2008, Vol. 36, No. 19 6048-6055
© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Stress-induced tRNA-derived RNAs: a novel class of small RNAs in the primitive eukaryote Giardia lamblia
Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory for Biocontrol, Zhongshan University, Guangzhou 510275, P. R. China
*To whom correspondence should be addressed. Tel: +86 20 84112399; Fax: +86 20 84036551; Email: lssqlh{at}mail.sysu.edu.cn
Correspondence may also be addressed to: lsszh{at}mail.sysu.edu.cn
Received July 25, 2008. Revised August 26, 2008. Accepted September 3, 2008.
Giardia lamblia is an early diverging and evolutionarily successful protozoan as it can enter into a dormant cyst stage from a vegetative trophozoite. During dormant stage, its metabolic rate decreases dramatically. However, to date, the regulatory molecules participating in the initiation and maintenance of this process have not been fully investigated. In this study, we have identified a class of abundant small RNAs named sitRNAs, which are 
46 nucleotides in length and accumulate in G. lamblia encysting cultures. Remarkably, they are derived from the 3' portion of fully matured tRNAs by cleavage of the anticodon left arm, with the 3' terminal CCA triplex still connected. During differentiation, only a limited portion of mature tRNAs is cleaved, but this cleavage occurs almost in the entire tRNA family. sitRNAs begin to accumulate as early as 3 h after initiation of encystation and are maintained at a relatively stable level during the whole process, exhibiting an expression peak at around 24 hr. Our studies further show that sitRNAs can be induced by several other stress factors, and in the case of serum deprivation, both tRNAs and sitRNAs degrade rapidly, with the accumulation of tRNA being halved. Our results may provide new insight into a novel mechanism for stressed G. lamblia to regulate gene expression globally.
Present address: Jun Luo, Henan Provincial Key Laboratory of Animal Immunology, Henan Academy of Agricultural Sciences, Zhengzhou 450002, P. R. China.
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