The nuclear envelope contains >100 transmembrane proteins that continuously 
exchange with the endoplasmic reticulum and move within the nuclear membranes. 
To better understand the organization and dynamics of this system, we compared 
the trafficking of 15 integral nuclear envelope proteins using FRAP. A 
surprising 30-fold range of mobilities was observed. The dynamic behavior of 
several of these proteins was also analyzed after depletion of ATP and/or Ran, 
two functions implicated in endoplasmic reticulum-inner nuclear membrane 
translocation. This revealed that ATP- and Ran-dependent translocation 
mechanisms are distinct and not used by all inner nuclear membrane proteins. The 
Ran-dependent mechanism requires the phenylalanine-glycine (FG)-nucleoporin 
Nup35, which is consistent with use of the nuclear pore complex peripheral 
channels. Intriguingly, the addition of FGs to membrane proteins reduces FRAP 
recovery times, and this also depends on Nup35. Modeling of three proteins that 
were unaffected by either ATP or Ran depletion indicates that the wide range in 
mobilities could be explained by differences in binding affinities in the inner 
nuclear membrane.