Figure 3.

The CO₂-responsive elements in the Ptca1 and Ptca2 promoters and the putative CO₂ signalling pathway. (a) Structures of the core-regulatory region of the Ptca1 and the Ptca2 promoter. (b) A suggested model of the cAMP-mediated CO₂ signalling pathway based upon the mammalian cAMP signalling cascade. (Redrawn from Matsuda & Kroth [82]). This model describes the signalling route under high CO₂ conditions. PDE, cAMP phosphodiesterase; PKA, protein kinase A; PKAC, C subunit of PKA; PP, protein phosphatase; CBP, CREB (cAMP binding protein) binding protein; DARPP, dopamine- and cAMP-regulated phosphoprotein. Parentheses indicate the number of candidate genes in the P. tricornutum genome. No functional analogue of DARPP has been identified so far.