Two proteins that roll the endoplasmic reticulum (ER) into tubes also help make nuclear pores, Dawson et al. reveal.
The pores are passageways into and out of the nucleus. Although researchers have worked out some of the mechanics of nuclear pore construction, they don't understand all of the events. Recent evidence suggested that some proteins that reside in the ER and nuclear envelope are involved. After screening about 70 ER and nuclear envelope proteins, the researchers took a closer look at two, Yop1 and Rtn1, that help curl flat ER membranes into tubes.
Deleting both genes from yeast cells produced obvious flaws in pore position, structure, and function, the researchers found. Normally scattered around the nuclear envelope, the pores clustered in one section of the membrane. And instead of spanning the nuclear envelope, many of the structures were stuck halfway in. These defects disrupted traffic into the nucleus. Using Xenopus nuclei, the researchers showed that blocking the vertebrate version of Rtn1 with an antibody also hindered pore formation.
The team concluded that ER-bending proteins are crucial for assembling new nuclear pores. Rolling up ER membranes and building nuclear pores might seem like very different jobs. But in both situations, the proteins have to deal with a curved membrane. At a nuclear pore, the inner and outer nuclear membranes fuse, creating a sharp bend. The researchers hypothesize that Yop1 and Rtn1 help stabilize this curved conformation.