group II intron, matK, chloroplast, splicing, regulation
Chloroplast genes of angiosperms contain about 20 group II introns that require numerous nuclear-encoded factors for their removal from precursor RNAs. Only one factor encoded by the chloroplast genome was suggested to be directly involved in splicing: MatK. MatK shares sequence similarities with maturases, bacterial splice factors encoded inside their target introns. For one such maturase called LtrA a direct interaction with its own mRNA resulting in translational repression has been demonstrated in a heterologous expression system in E. coli. We used this expression system to test the influence of the expression of Zea mays MatK on the expres-sion of a reporter gene under the control of putative maize matK regulatory sequences. We show that chloroplast-derived sequences devoid of bacterial translational signals are translated efficiently in E. coli. However, when MatK is co-expressed with reporter gene constructs, no evidence for repression or activation of the reporter was detected, demonstrating that chloroplast MatK is not sufficient to influence its own gene expression at least not in this heterologous system.