Expression of the ribulose-1,5-bisphosphate carboxylase large subunit gene and three small subunit genes in two cell types of maize leaves.

Transcripts of three distinct ribulose-1,5-bisphosphate carboxylase (RuBPC) small subunit (SS) genes account for approximately 90% of the mRNA for this protein in maize leaves. Transcripts of two of them constitute >80% of the SS mRNA in 24-h greening maize leaves. The third gene contribute approximately 10%. Transcripts of all three nuclear-encoded SS genes are detectable in bundle sheath (BSC) and mesophyll cells (MC) of etiolated maize leaves. The level of mRNA for each gene is different in etioplasts of MC but all drop during photoregulated development of chloroplasts in MC and follow a pattern of transitory rise and fall in BSC. The amounts of LS and SS proteins continue to increase steadily well after the mRNA levels reach their peaks in BSC. The molar ratio of mRNA for chloroplast-encoded RuBPC large subunit (LS) to the nuclear genome encoded SS is about 10:1 although LS and SS proteins are present in about equimolar amounts.