The yeast ARS-1 element contains a scaffold attachment region (SAR) that we have previously shown can bind to plant nuclear scaffolds in vitro. To test effects on expression, constructs in which a chimeric P-glucuronidase (GUS) gene was flanked by this element were delivered into tobacco suspension cells by microprojectile bombardment. In stably transformed cell lines, GUS activity averaged 12-fold higher (24-fold on a gene copy basis) for a construct containing two flanking SARs than for a control construct lacking SARs. Expression levels were not proportional to gene copy number, as would have been predicted if the element simply reduced position effect variation. Instead, the element appeared to reduce an inhibitory effect on expression in certain transformants containing multiple gene copies. The effect on expression appears to require chromosomal integration, because SAR constructs were only twofold more active than the controls in transient assays.

To measure transcript levels for individual members of the Cab (chlorophyll a/b protein) multigene family in pea under a range of developmental situations, we developed a system using cDNA synthesis, the polymerase chain reaction (PCR), and chemiluminescence detection. In order to design gene-specific PCR primers for all genes, a partial genomic clone for a fifth, Type I LHCII (light-harvesting complex of photosystem II) gene, Cab-9 The Cab-9 sequence appears in the Genbank/EMBL databases under the accession number M86906 , was isolated and sequenced. All seven known Cab genes in pea are expressed in light-grown buds and leaves, including several genes previously known only from genomic clones. There appear to be at least two groups of Cab genes in pea which differ in their response to light and development. The first group (consisting of Cab-8, AB96, Cab-215 and Cab-315) includes Type I, Type II and Type III genes, shows a relatively strong response to red light, and has bud transcript levels similar to or slightly higher than leaves. The second group, consisting of the Type I genes Cab-9, AB80 and AB66, shows little or no transcript accumulation 24 h after a red light pulse, and has higher transcript levels in leaves than in buds. Transcript levels for genes in this second group appear to be lower than those of the first group in all developmental situations examined. These data indicate that there has been an evolutionary divergence of the responses to light and development among the Type I LHCII genes.