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Unformatted text preview: Cell membrane Cytoskeletal element Localized mRNA for transcription factor Newly translated transcription factor Direction of protein diffusion Cell sheet (developmental field) (a) (b) (1) (2) (3) (4) (1) (2) (3) (4) (5) Cell secreting positional- information signal Activated signal- transduction pathway Low-level activation Low-level activation High level of transcription- factor activation Receptor for signal Figure 18-19 The two general classes of positional information. (a) Asymmetrical organization of the cytoskeletal system permits localization of mRNA encoding a transcription factor that will provide positional information. Translation of the anchored mRNA will lead to diffusion of the newly translated transcription factor and the formation of a transcription-factor gradient with a high point near the site of the mRNA. (b) Secretion of a positional-information signaling molecule from a localized source (cell) activates the signal-transduction apparatus and the target transcription factors according to the level...
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- Spring '08