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In the Lab

By Carol L. Dieckmann, Ph.D.

The two major projects being pursued in the lab can be described under the heading "organelle biogenesis". Understanding mitochondrial RNA metabolism in yeast is one of our goals. There are only seven messenger RNAs in yeast mitochondria. Each of the seven mRNAs interacts with one or more message-specific proteins, which promote processing, stability and translation of the RNA. We are studying in detail how one such protein, Cbp1, interacts with the mRNA encoding cytochrome b. Cbp1 both promotes the stability of the mRNA and is required for translation. Both biochemical and genetic approaches are being used in conjunction to further define this interaction. Recently we have broadened our focus to try to understand the general factors and rules for mitochondrial mRNA processing and turnover. Understanding how eyespots are assembled and placed asymmetrically in algal cells is our other goal. Eyespots in the single-celled alga Chlamydomonas allow the cells to sense light intensity and direction.

The organelle sends signals to the flagella to direct phototaxis. Eyespots are formed de novo after every cell division. The chloroplast and cell collaborate to form the eyespot, which is a tightly layered sandwich of four different membrane types and carotenoid pigment granules. The eyespot always forms midway between the two cell poles, one pole defined by the attachment of the flagella. And, the eyespot always forms 45° from the flagellar plane, clockwise of the flagellum formed in the last cell division. Through mutagenesis, we have identified three genes that are required for the proper assembly of the eyespot and a fourth gene that is required for proper placement. The most abundant eyespot proteins are being characterized by mass spectrometry. We will continue to use genetics and biochemistry to understand how this interesting structure is built and placed at each cell division.