A NOVEL SUBVIRAL AGENT ASSOCIATED WITH A GEMINIVIRUS - THE FIRST REPORT OF A DNA SATELLITE

Numerous plant RNA viruses have associated with them satellite (sat) R NAs that have little or no nucleotide sequence similarity to either th e viral or host genomes but are completely dependent on the helper vir us for replication, Wt report here on the discovery of a 682-nt circul ar DNA satellite associated with tomato leaf curl geminivirus (TLCV) i nfection in northern Australia, This is the First demonstration that s atellite molecules are not limited to RNA viral systems, The DNA satel lite (TLCV sat-DNA) is strictly dependent for replication on the helpe r virus replication-associated protein and is encapsidated by TLCV coa t protein, It has no significant open reading frames, and it shows no significant sequence similarity to the 2766-nt helper-virus genome exc ept for two short motifs present in separate putative stem-loop struct ures: TAATATTAC, which is universally conserved in all geminiviruses, and AATCGGTGTC, which is identical to a putative replication-associate d protein binding motif in TLCV Replication of TLCV sat-DNA is also su pported by other taxonomically distinct geminiviruses, including tomat o yellow leaf curl virus, African cassava mosaic virus, and beet curly top virus, Therefore, this unique DNA satellite does not appear to st rictly conform with the requirements that dictate the specificity of i nteraction of geminiviral replication-associated proteins with their c ognate origins as predicted by the current model of geminivirus replic ation.