How can I search for the S. cerevisiae ortholog(s)/homolog(s) of an S. pombe gene?

In PomBase, S. cerevisiae orthologs are curated for S. pombe genes as described in the Orthologs documentation.

To find S. pombe orthologs for a budding yeast gene, you can search for the systematic name (ORF name) of the S. cerevisiae gene in the Simple Search (go to http://www.pombase.org/search/ensembl or use the search box in the page header). For example, S. cerevisiae LRP1 has the systematic name YHR081W, and a search on this in PomBase will retrieve the S. pombe gene cti1. Note that only systematic names can be searched for S. cerevisiae, to avoid confusion in cases where unrelated genes coincidentally have the same name in S. pombe and S. cerevisiae. To find systematic names of S. cerevisiae genes, you can search SGD.

Also see the FAQ on downloading the full set of orthologs.