Catalyzes the acetylation of L-2,4-diaminobutyrate (DABA) to gamma-N-acetyl-alpha,gamma-diaminobutyric acid (ADABA) with acetyl coenzyme A. acetyl-CoA + L-2,4-diaminobutanoate = (2S)-4-acetamido-2-aminobutanoate + CoA + H(+) Amine and polyamine biosynthesis; ectoine biosynthesis; L-ectoine from L-aspartate 4-semialdehyde: step 2/3. Belongs to the acetyltransferase family. EctA subfamily.