Abstract: We describe the generation of null-mutants of 12 open reading frames (ORFs), discovered during the systematic sequencing of the Saccharomyces cerevisiae genome. These ORFs are located on chromosome IV (YDL183c), on chromosome VII (YGL139w, YGL140c, YGL141w, YGR280c and YGR284c) or on chromosome XIV (YNL006w, YNR004w, YNR007c, YNR008w, YNR009w and YNR013c). Disruptants were generated using the PCR-based short flanking homology (SFH) strategy in yeast strain FY1679. Tetrad analysis, following sporulation of the heterozygous disruptants, revealed that YGR280c and YNL006w are essential genes for vegetative yeast growth in rich medium. The lethality of the two genes was confirmed by gene complementation analysis. The protein encoded by YNL006w (LST8) is now known to be involved in transport of permeases from the Golgi to the plasma membrane. Basic phenotypic analyses were performed on haploid disruptants from both mating types of 10 non-essential genes. One disruptant (YNR004w) revealed a slow growth rate on glucose-minimal medium at 15 degrees C. For each of the individual ORFs, a disruption cassette and the corresponding cognate gene were cloned into appropriate plasmids.CI - Copyright 2002 John Wiley & Sons, Ltd.