Asus Z270G : https://www.asus.com/us/Motherboards/ROG-STRIX-Z270G-GAMING/specifications/
it states
1 x M.2 Socket 3, with M key, type 2242/2260/2280 storage devices support (SATA & PCIE 3.0 x 4 mode)
1 x M.2 Socket 3, with M key, type 2242/2260/2280/22110 storage devices support (PCIE 3.0 x 4 mode)
Asus Z270G : https://www.asus.com/us/Motherboards/ROG-STRIX-Z270G-GAMING/specifications/
it states
1 x M.2 Socket 3, with M key, type 2242/2260/2280 storage devices support (SATA & PCIE 3.0 x 4 mode)
1 x M.2 Socket 3, with M key, type 2242/2260/2280/22110 storage devices support (PCIE 3.0 x 4 mode)