The transport vesicle budding from the endoplasmic reticulum contain
at least two types of v-SNAREs, those that target the vesicles to the
cis Golgi network, and those that are in transit to the trans Golgi
network.
 Why might this be a problem?

Does this answer your question?

http://www.nature.com/cgi-taf/DynaPage.taf?file=/emboj/journal/v16/n11/abs/7590283a.html&dynoptions=doi1076618460

Regards;
tutuzdad-ga

I think that you can find your answer here:

http://www.uoguelph.ca/botany/courses/BIOL2210/lectures19-20_2001w.htm

>The transport vesicle budding from the endoplasmic reticulum contain
>at least two types of v-SNAREs, those that target the vesicles to the
>cis Golgi network, and those that are in transit to the trans Golgi
>network.
> Why might this be a problem?

The problem is that v-SNAREs are part of the targeting mechanism for
these vesicles.

The normal order of movement of the vesicles is to go from the
ER-->cis-Golgi-->trans-Golgi.

Various posttranslational modifications (typically covalent linkage of
carbohydrate moeities that help these proteins maintain a long
half-life) are made to proteins within these vesicles as they move
through the Golgi.  If there are 2 types of v-SNAREs on the vesicles
as they leave the ER, then you would naively think that the vesicles
might directly fuse with the TRANS-golgi without ever going through
the CIS-golgi, thereby causing their cargo (secreted proteins) to miss
out on whatever carbohydrate attachments were supposed to be added to
them in the cis-golgi.  The implication is that there must be some
additional targeting information present on these vesicles that makes
them fuse with the proper (cis) portion of the Golgi.

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=129673

decent explanation of what people think about snares