The presently disclosed subject matter provides compositions and methods comprising improvements of a CRISPR system (e.g. CRISPR associated (Cas) 9 (CRISPR-Cas9, non-Cas9 CRISPR systems). Such compositions may comprise modifications to the H1 promoter region, addition of 5′UTR modifications, different orthologous sequences of the H1 promoter, novel compact bidirectional promoter sequences with both pol II and pol III activity, addition of Kozak consensus sequences, termination sequences, addition of conditional pol II/pol III bidirectional promoter expression, addition of a donor template sequence for correcting mutations, or combinations thereof. Other aspects of the invention relate to modifications to Cas9 through post-transcriptional cell-cycle regulation fusions, engineered partial target sites such that the nuclease can bind without DNA cleavage, auto-regulation sites, and N-terminal modifications to modulate half-life.