tRNA是蛋白质翻译机器中的必需成分，它对细胞的生长和增殖及器官的发育起着决定性作用。tRNA生物合成包括tRNA基因的转录、转录后的加工和修饰。对tRNA生物合成的研究还包括tRNA在细胞中的运输、tRNA生物合成的质量监控及其与其他重要细胞途径（如mRNA生物合成、DNA损伤应答和细胞周期）之间的相互作用，以及tRNA生物合成在生长发育和疾病中的作用。本文主要介绍了近年来真核生物细胞质tRNA生物合成研究的一些重要进展。

芽殖酵母（Saccharomycescerevisiae）和裂殖酵母（Schizosaccharomycespombe）是用来研究异染色质形成、细胞周期、DNA复制等重要细胞功能的理想单细胞真核生物。本文主要介绍这2种酵母中异染色质形成的机制。异染色质是一种抑制基因转录和DNA重组的特殊染色质结构。尽管在芽殖酵母和裂殖酵母中异染色质形成都需要组蛋白修饰，但异染色质建立的机制不同。在芽殖酵母中参与异染色质形成的主要蛋白是Sir124蛋白（其中Sir2为组蛋白H3去乙酰化酶），而组蛋白H3赖氨酸9甲基化酶Clr4和异染色质蛋白Swi6在裂殖酵母异染色质形成中起关键的作用。在这两个酵母中，参与异染色质形成的组蛋白修饰蛋白由DNA结合蛋白招募到异染色质。此外，裂殖酵母也利用RNA干扰系统招募组蛋白修饰蛋白。

tRNA在蛋白质合成过程中起着极其重要的作用。在所有的生物体内，tRNA首先以前体形式转录，然后必需经过一系列的加工后才能成为有功能的tRNA分子。tRNaseZ、RNaseP和tRNA剪接内切酶是参与tRNA前体加工的三种主要的核酸内切酶，分别参与tRNA前体3'末端、tRNA前体5'末端和内含子剪接的加工。这三种酶具有不同的结构特征，并且利用完全不同的催化机制水解磷酸二酯键。tRNaseZ和RNaseP都是金属酶，活性中心分别需要Zn2＋和Mg2＋的参与；而tRNA剪接内切酶活性中心不需要金属离子，是一个由不同催化亚基上的关键氨基酸残基构成的组合式活性中心。

Termination by RNA polymerase III (Pol III) produces RNAs whose 3 oligo(U) termini are bound by La protein, a chaperone that protects RNAs from 3 exonucleases and promotes their maturation. Multiple reports indicate that yeasts use La-dependent and -independent pathways for tRNA maturation, with defective pre-tRNAs being most sensitive to decay and most dependent on La for maturation and function. The Rpc11p subunit of Pol III shows homology with the zinc ribbon of TFIIS and is known to mediate RNA 3 cleavage and to be important for termination. We used a La-dependent opal suppressor, tRNASerUGAM, which suppresses ade6-704 and the accumulation of red pigment, to screen Schizosaccaromyces pombe for rpc11 mutants that increase tRNA-mediated suppression. Analyses of two zinc ribbon mutants indicate that they are deficient in Pol III RNA 3 cleavage activity and produce pre-tRNASerUGAM transcripts with elongated 3 -oligo(U) tracts that are better substrates for La. A substantial fraction of pre-tRNASerUGAM contains too few 3 Us for efficient La binding and appears to decay in wild-type cells but has elongated oligo(U) tracts and matures along the La-dependent pathway in the mutants. The data indicate that Rpc11p limits RNA 3 -U length and that this significantly restricts pre-tRNAs to a La-independent pathway of maturation in fission yeast.

The RNA polymerase (pol) III-transcribed (e.g. tRNA and 5S rRNA) genes of traditionally studied organisms rely on gene-internal promoters that precisely position the initiation factor, TFIIIB, on the upstream promoter-less DNA. This is accomplished by the ability of the TFIIIB subunit, TFIIB-related factor (Brf1), to make stable protein±protein interactions with TATA-binding protein (TBP) and place it on the promoter-less upstream DNA. Unlike traditional model organisms, Schizosaccharomyces pombe tRNA and 5S rRNA genes contain upstream TATA promoters that are required to program functional pol III initiation complexes. In this study we demonstrate that S.pombe (Sp)Brf does not form stable interactions with TBP in the absence of DNA using approaches that do reveal stable association of TBP and S.cerevisiae (Sc)Brf1. Gel mobility analyses demonstrate that a TBP±TATA DNA complex can recruit SpBrf to a Pol III promoter. Consistent with this, overproduction of SpBrf in S.pombe increases the expression of a TATA- ependent, but not a TATA-less, suppressor tRNA gene. Since previous whole genome analysis also revealed TATA elements upstream of tRNA genes in Arabidopsis, this pathway may be more widespread than appreciated previously.