Celenza, J.L., L. Marshall-Carlson, & M. Carlson (1988) The yeast SNF3 gene encodes a glucose transporter homologous to the mammalian protein. Proc. Natl Acad. Sci. USA 85: 2130-2134.

1. Bioinformatics is a rapidly expanding field that includes computer scientists and molecular biologists working together to improve methods of storing and accessing sequence and structure information in biological databases. The authors of this article use sequence analysis to identify possible functions of the Snfi protein.

(a) What is a hydrophobicity profile and why does this analysis of Snf3 protein suggest that it is an integral membrane protein?

(b) This study and others showed that Snf3p exhibits structural and functional homology to glucose, arabinose, xylose, maltose, and galactose transport proteins from various organisms such as humans, E. coli, and several different species of yeast. All of the genes encoding these proteins could be said to fall into a multigene family of transporters of what class of molecules?

2. Diagram the three fusion genes SNF3(3)-lacZ, SNF3(321 )-lacZ, and SNF3(797)-lacZ. Be sure to clearly indicate how the three differ from one another.

3. Describe the two methods (cofractionation and indirect immunofluorescence) used to show that Snf3 protein localizes to the plasma membrane. What is the 'probe' used to detect the Snf3-LacZ fusion protein in indirect immunofluorescence?

4. The following questions explore the structure/function analysis carried out on Snf3p.

(a) What portion of the Snf3 protein is responsible for membrane localization?

(b) What portion of the Snf3 protein is unique compared with the human glucose transporter?

(c) Is this unique region required for Snf3p function and how do the authors test this? Be careful. Note the location of codon 797 in Snf3p!

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