The transmembrane region of the protein is likely to have-
The transmembrane proteins lie similar to that of the lipid bilayer. The lipid bilayer is hydrophilic in the outer and the inner parts and has a hydrophobic core. 
Similarly, the transmembrane proteins have outer and inner ends which are hydrophilic and a core which is hydrophobic. 
So the transmembrane region of the protein is hydrophobic.
A stretch of hydrophilic amino acids
A stretch of hydrophobic amino acids
A disulphide loop
Alternating hydrophilic and hydrophobic amino acids