The large amount of available genome sequencing data presents a huge challenge in the form of orphan sequences. This study reports the detailed functional characterization of one such orphan sequence in Schizosaccharomyces pombe. We identified this gene as a prominently upregulated 1.4 kb transcript in a screen for Cigarette smoke extract responsive genes in S. pombe and named it Stress Responsive Orphan 1 (Sro1). We report various functions of Sro1 in regulation of cellular behaviour under stress conditions. We show that this gene (Sro1) responds to a variety of stress conditions and that the expression of the gene is regulated mainly through the stress activated protein kinase (SAPK) Sty1 and its downstream transcription factor Atf1. Deletion of Sro1 also significantly alters the reactive oxygen species (ROS) generation profiles and the cell-cycle progression of S. pombe during stress conditions. The stress-specific alteration of the ROS generation profiles and checkpoint activation resulting from deletion of the gene suggest that Sro1 might be a key player in determining cellular responses/fate under stress conditions. © 2008 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.