E means Electromagnetic Iris Mechanism
An electromagnetic iris mechanism in the lens directly controls the iris blades with a servo. This ensures a particularly high level of precision and consistency of exposure, which is especially useful for fast continuous shooting. With conventional lenses, including type G and D, the diaphragm blades are controlled from the camera body via a mechanical coupling.

G means NIKKOR type G lens (This is explained a little better in the English Glossary).
G-NIKKORE lenses do not have an aperture ring. The aperture is adjusted on the camera body.

Nikon Lens Glossary (German):
http://www.nikon.de/de_DE...

Nikon Lens Glossary (English):
https://support.nikonusa.com/app...