Catalyzes the reaction of 4-carboxy-5-aminoimidazole ribotide (CAIR) and aspartic acid with the formation of N-succinyl-5-amino-imidazole-4-carboxamide ribotide (SAICAR) in the purine biosynthesis pathway. 5-amino-1-(5-phospho-D-ribosyl)imidazole-4-carboxylate + ATP + L-aspartate = (2S)-2-[5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamido]succinate + ADP + 2 H(+) + phosphate Purine metabolism; IMP biosynthesis via de novo pathway; 5-amino-1-(5-phospho-D-ribosyl)imidazole-4-carboxamide from 5-amino-1-(5-phospho-D-ribosyl)imidazole-4-carboxylate: step 1/2. Monomer. Present with 4280 molecules/cell in log phase SD medium. Belongs to the SAICAR synthetase family.