"we isolated a nuclear regulatory gene, Ccm1, encoding a 699-aa hydrophilic protein with a putative zinc-finger motif in its N-terminal region and a Gln repeat characteristic of transcriptional activators"

"Introduction of Ccm1 into this mutant restored an active carbon transport through the CCM, development of a pyrenoid structure in the chloroplast, and induction of a set of CCM-related genes."

"These data indicate that Ccm1 is essential to control the induction of CCM by sensing CO2 availability in Chlamydomonas cells."

"revealed that His-54 within the putative zinc-finger motif of the CCM1 is crucial to its regulatory function"

"The cia5 mutant is defective in all of these phenotypes. A newly isolated gene, designated Cia5, restores transformed cia5 cells to the phenotype of wild-type cells."

"It encodes a protein that has features of a putative transcription factor and that, likewise, is present constitutively in low and high CO2 conditions."

"cia5 mutants complemented with the truncated gene exhibit constitutive synthesis of mRNAs from CO2-responsive genes in light under both high and low CO2 conditions"

"These discoveries suggest that posttranslational changes to the C-terminal domain control the ability of CIA5 to act as an inducer and directly or indirectly control transcription of CO2-responsive genes."

"It is concluded that this mutant fails to induce the CO(2) concentrating system and is incapable of adapting to low CO(2) conditions."

"It was found that 1 mol of zinc is bound to 1 mol of amino acid regions 1-71 and 72-101 of CCM1, respectively."

"amino acid residues such as C36, C41, H54, C77, C80, H90 and C93 were indispensable for induction of the CCM in response to Ci-limiting stress conditions"

"CCM1 is present as a protein complex of approximately 290-580 kDa independent of Ci availability"

"The fact that the induction of almost all low-CO2 inducible genes was impaired in the ccm1 mutant suggests that CCM1 is a master regulator of CCM through putative low-CO2 signal transduction pathways."

"We observed a massive impact of CIA5 and CO 2 on the transcriptome, affecting almost 25% of all Chlamydomonas genes"

"Expression of most putative C i transporters and induced CAs requires CIA5, even though the expression of CIA5 itself does not depend on the CO 2 level, so posttranslational activation of CIA5 in low CO 2 apparently is required for CIA5 to regulate these genes"

"CIA5 has been proposed to be a transcription regulator ( Fukuzawa et al., 2001 ; Xiang et al., 2001 ), but we know very little about sequences recognized by its putative DNA binding domain or the genes it directly regulates downstream."

"Confocal microscopy revealed strong nuclear signals in both transformants under HC and VLC conditions (Fig. 3A)."

"Notably, the nuclear localization pattern remained unchanged between HC and VLC conditions for both proteins, showing punctate nuclear signals characteristic of transcription factor localization (Fig. 3A)."

"Although CCM1 contains two Zn2+-binding sites (13, 14), direct DNA binding has not been demonstrated, suggesting that CCM1 operates in conjunction with other nuclear factors."

"CBP1 colocalizes and interacts with CCM1 in the nucleus regardless of CO2 conditions."

"We demonstrate that CIA5 is constitutively expressed regardless of Zn supply, but its encoded protein undergoes proteasomal degradation under Zn deficiency, providing a checkpoint that prevents CCM induction when Zn cofactors are unavailable."

"We identified a COBW domain-containing GTPase, ZNG3, as a constitutive interacting partner of CIA5."

"One such example is CIA5, which contains two Zn‐binding sites within the first 110 amino acids, one in a C2H2 zinc finger between amino acids 35 and 70, and the second between amino acids 70 and 100"

"CIA5 localizes to the nucleus, and cia5 mutants fail to transcriptionally induce Ci transporter genes, CAHs, and many genes encoding structural components of the CCM"

"Earlier studies did not detect direct DNA binding by CCM1/CIA5, but recent in vitro work using purified full-length CIA5 demonstrated specific binding to a GC-rich motif found in promoters of CIA5-dependent genes (Chen and Spalding, 2026)."

"The Chlamydomonas transcriptional regulator CCM1/CIA5 appears to be a lineage-restricted component rather than a broadly conserved green-plant regulator."

"The primary CO2/HCO3− sensor upstream of CCM1/CIA5 remains unknown."

"Finally, we show that the CCM regulator CIA5 also regulates photoprotection, controlling LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 protein accumulation."

"This phenotype was fully reversed by ectopic expression of the WT CIA5 gene (Fig. 3a)."

"Comparison of Volvox and Chlamydomonas CCM1 revealed a highly conserved N-terminal region containing zinc-binding amino acid residues, putative nuclear localization and export signals, and a C-terminal region containing a putative LXXLL protein-protein interaction motif."