Curr Genet (2009) 55:511–520 DOI 10.1007/s00294-009-0262-x 123 RESEARCH ARTICLE The pleiotropic cell separation mutation spl1-1 is a nucleotide substitution in the internal promoter of the proline tRNA CGG gene of Schizosaccharomyces pombe Ida Miklos · Katalin Ludanyi · Matthias Sipiczki Received: 18 May 2009 / Revised: 6 July 2009 / Accepted: 9 July 2009 / Published online: 28 July 2009  Springer-Verlag 2009 Abstract spl1-1 was originally identiWed as a spontane- ous mutation genetically interacting with sep1-1 and cdc4-8 in producing multinucleate syncytia. This study shows that it is allelic with the proline-tRNA CGG gene SPATRN- APRO.02. Its nucleotide sequence contains a C!T substi- tution in the region corresponding to the B-box of the putative intragenic promoter and the TC loop of the mature tRNA. The substitution drastically reduces the tran- scription eYciency of the gene and pleiotropically aVects numerous cellular processes. spl1-1 cells are temperature sensitive, osmosensitive, bend at higher temperatures, have extended G2 phase and are defective in cell separation (sep- tum cleavage). The proline-tRNA TGG gene SPATRN- APRO.01 can partially suppress the spl1-1 mutation when introduced into the cells on a multicopy plasmid. The eVect of a mutation in a tRNA gene on cell separation brings a new element into the complexity of the regulation of cell division and its co-ordination with other cellular processes in Schizosaccharomyces pombe. Keywords Cytokinesis · Septum · Transcription · Cell cycle · Fission yeast · tRNA Introduction The cells of the Wssion yeast Schizosaccharomyces pombe divide by medial septation followed by septum cleavage. The septum is a three-layer structure, which grows centrip- etally and divides the cell into two daughter cells (Johnson et al. 1973). The daughter cells then degrade the mother cell wall at its junction with the septum and subsequently also one of the three septal layers, the so-called primary septum, to separate from one other. The process requires the directed activity of the exocyst system to deliver the 1,3--glucanase Agn1 (Dekker et al. 2004; Garcia et al. 2005) and the endo--1,3-glucanase Eng1 (Martin-Cuadrado et al. 2003) to the site of polysaccharide degradation, as well as the turgor-generated force that facilitates the split of the primary septum through bulging out of the secondary septa (reviewed in Sipiczki 2007). Since cell separation is not a vital function, the mutants defective in septum split- ting are viable, but form hyphae instead of separate yeast cells (Sipiczki et al. 1993). The genetic analysis of a large group of cell separation (hyphal) mutants identiWed 16 cell separation (designated sep or spl) genes (Sipiczki et al. 1993; Grallert et al. 1997, 1999). Five sep genes encode proteins involved in transcription. sep1 + codes for a fork-head type transcription factor, the products of the sep10 + , sep11 + and sep15 + genes are Medi- ator subunits, whereas the Sep9p protein is a SAGA subunit (for a review see Sipiczki 2007). Mediator and SAGA are general transcription factors that are required for the tran- scription of large groups of genes, not only of those involved in cell separation (Miklos et al. 2008; Batta et al. 2009). The Sep1p transcription factor participates in a checkpoint-like mechanism that co-ordinates nuclear divi- sion and septation (Grallert et al. 1998) and regulates many M phase-speciWc genes (Rustici et al. 2004). The sep1-1 Communicated by C. HoVman. I. Miklos · M. Sipiczki (&) Department of Genetics and Applied Microbiology, University of Debrecen, P.O. Box 56, 4010 Debrecen, Hungary e-mail: lipovy@tigris.unideb.hu K. Ludanyi Department of Immunology, University of Debrecen, 4010 Debrecen, Hungary