AbstractA genetic screen for synthetic lethal interactions with arf1− identified a recessive mutation in TRS130, one of 10 components in the trafficking protein particle (TRAPP) complex (Sacher et al., 2000). As TRS130 is an essential gene, the synthetic lethal allele (trs130‐101) is a novel one that requires ARF1 for viability. This allele was found to exhibit no defects in secretory function, i.e. processing of carboxypeptidase Y or invertase. YPT31 and YPT32 were identified in a subsequent screen as high‐copy suppressors of arf1−trs130‐101. Increasing the gene dosage of YPT31/32 also suppressed lethality resulting from deletion of TRS130 or TRS120 but not three other essential TRAPP subunit‐encoding genes. Although unable to suppress defects in several alleles of ARF1, increasing the gene dosage of YPT31/32 suppressed the cold sensitivity of gcs1−, an Arf GTPase‐activating protein (GAP). Thus, these genetic interactions provide initial evidence for linkage of Arf and TRAPP signalling and for Ypt31/32 proteins functioning downstream of both components in the TRAPP complex and of Arf signalling via the Gcs1 Arf GAP. Copyright © 2002 John Wiley & Sons, Ltd.