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Unformatted text preview: Fee c®’_\ @ohatm J»© (est hdoidCCQ © © Coniugation i Sporulafion ® Germination G ermination Figure 4.19. Life cycle of Saccharomyces caret/fares. S. cerevisiae can reproduce asexuaily by budding. as either haploid or diploid cells. Haploid cells exist in two mating types a and o and they can mate to form diploid cells. Cells of opposite mating types secrete mating factors (pheromones) that bind to receptors on each others' surface. This chemical signalling induces cell cycle arrest and the expression of genes that carry out the physical process of mating. It stewed of nitrogen. the diploid ceils will sporulate to yield feur haploid spores. These germinate to form haploid budding cells that can mate with each other to restore the diploid state. From 771a Cat! Cycfe: an introduction by A. Murray and 1'. Hunt. Copyright © 1993 by A. Murray and T. Hunt. Used by permission of Oxtord University Press. lnc. Localized exocytosis and wall expansuon Chitin ring. neck filaments / Vesicle translocatipn and targeting Figure 4.1. Physiology of bud growth in yeast. The diagram identities processes known or surmised to contribute to the enlargement of the buds suriace. Reproduced with permission from Harold [1995}. and the Society ior General Microbiology. AXIAL BIPOLAR 0 Incl o: CELLS UuCELLS Figure 4.2. Bud site selection patterns in S. cerew‘srae. Left: in axial budding. the mother oell {M} buds imme- diately adjacent to its last daughter; the daughter cell [Di buds toward its mother. Right: in bipolar budding. the mother cell can bud at Dr near either of its poles; the daughter cell buds away from its mother. The arrows within the cells in the figure indicate the axis of polarity and cell division. The bud produced by the mother cell is drawn longer than the bud irom its daughter cell because mother cells initiate budding before daughter cells. Reproduced with permission from Chant and Herskowitz {1991i G“.- Cell Press. HMLo MATa HMRa OFF ON OFF L ‘11) + usg . l storage locus playback locus storage locus _ mating — v 1 -2 —l as . . . Al 052 l g as 5'5 Cassette replaced Transposrtion W MA Tr: hsg I| l . ' HMLo MATa HMRs melOSlS [,1 ,7. __________- _—_—;— —_'_—;—_'_; _ _ _ OFF ON 0;; a cell 039 i-—- 200 no —~l-—— 150 no ———a1 w- vvun- mating HO. 9. Cassette mechanism for mating-type interconversion. 31 Q1) asg The top line shows the arrangement of cassettes on chromosome [ll _—_..._ -' as a in an a cell. The cassette at MAT is expressed: those located at MA Ta W“ HML and HMR are repressed by Sir. Switching to a occurs by hSQ I removing the a cassette from MAT and replacing it by information I ."m HMRa. The central regions of the cassettes tshown as striped l [-055 open rectangles: represent distinct nucleotide sequences. The . me I Minn from the a cassette tthe so-called Ya region] is 741 base pairs: - - ' — — —— ' t the region from the a cassette tthe Ya region: is 642 base pairs 12. ' i 107. 1431. The regions adjacent to the Y region (the X and 2 regions. 8H1 09“ i which are approximately 700 base pairs: are involved in the recom- (139 1 bination between cassettes at HML or HMR loci and the mating- 1 “2 i no type locus. Mating-type interconversion is initiated by the product or - - [— tt2 —| 3.5 of the H0 gene. which codes for an endonuclease that produces a _'_" 1— ' *— g mating double-strand break at MAT l'lS. 146i. Subsequent repair of the K x" double-strand break leads to a duplicative transposition of informa- '\31__l “2 l _' hsg tion from HML or HMR to MA 1'. The distance between MAT and a1 ' . Him. is approximately 200 kilobases tltbl um. 14?): the distance —-—— meiosis between Malde HMR is approximately 150 kilobaaes {110). F igure 2 Control of oell-typc-spccific gene sets by regulatory proteins encoded by the mating-type locus. The three pancls show how the regulatory proteins on- coded by the mating-type locus (Matotlp, MataZp,.Matalp-Matt12p) govefrn transcription of three different gene sets (053, ct-spectfic genes; tug, a-spec1 to genes; and lug, haploid-specific genes}. Transcription is Indicated by a wavy :1:- row: lines with blund heads indicate inhibition, lines with paint arrowheads In t- cate stimulation. Matct] p activates transcription of the a—specnfic genes; MataZp represses transcription of the a-specil'ic genes; Matalp-Matoth represses t_ran- scription of the haploid-specific genes. ’11": .II' la" la} a'. \ / . . \ _. .. -a_ not; kn,- Figure :0 Switching pattern of homothallic yeast: A mitotic lineage of yeast cells that are: able to switch mating type. Asterisks indicate cells that are com- petent to switch mating type in their next cell division. As described in the text, only cells that have previously budded are competent. The initial cell (S) is a spore that carries H0 and can thus exhibit high frequency of mating-type inter- conversion. This cell germinates and, after its first cell division, yields two cells (5 and its first daughter, Di), which are invariably or. In the next cell division. the 5 cell typically (in ~75% of its cell divisions) gives rise to two cells (5 and D2) that have switched to a. The 91 cell at the tWo-cell stage invariably gives rise to two (1 cells, but in its next division (to produce cells D! and 131-1), it can yield 3 cells. (Adapted from Strathcrn and Herskowitz 1979.) ...
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This note was uploaded on 06/11/2009 for the course MIC 170 taught by Professor Shiozaki during the Spring '09 term at UC Davis.

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