diff --git a/bwamem.c b/bwamem.c
index 52dc7fb..7efbb8d 100644
--- a/bwamem.c
+++ b/bwamem.c
@@ -715,20 +715,29 @@ mem_alnreg_v mem_align1_core(const mem_opt_t *opt, const bwt_t *bwt, const bntse
 	return regs;
 }
 
-mem_alnreg_v mem_align1(const mem_opt_t *opt, const bwt_t *bwt, const bntseq_t *bns, const uint8_t *pac, int l_seq, char *seq)
-{ // the difference from mem_align1_core() lies in that this routine calls mem_mark_primary_se()
+mem_alnreg_v mem_align1(const mem_opt_t *opt, const bwt_t *bwt, const bntseq_t *bns, const uint8_t *pac, int l_seq, const char *seq_)
+{ // the difference from mem_align1_core() is that this routine: 1) calls mem_mark_primary_se(); 2) does not modify the input sequence
 	mem_alnreg_v ar;
+	char *seq;
+	seq = malloc(l_seq);
+	memcpy(seq, seq_, l_seq); // makes a copy of seq_
 	ar = mem_align1_core(opt, bwt, bns, pac, l_seq, seq);
 	mem_mark_primary_se(opt, ar.n, ar.a);
+	free(seq);
 	return ar;
 }
 
 // This routine is only used for the API purpose
-mem_aln_t mem_reg2aln(const mem_opt_t *opt, const bntseq_t *bns, const uint8_t *pac, int l_query, uint8_t *query, const mem_alnreg_t *ar)
+mem_aln_t mem_reg2aln(const mem_opt_t *opt, const bntseq_t *bns, const uint8_t *pac, int l_query, const char *query_, const mem_alnreg_t *ar)
 {
 	mem_aln_t a;
-	int w2, qb = ar->qb, qe = ar->qe, NM, score, is_rev;
+	int i, w2, qb = ar->qb, qe = ar->qe, NM, score, is_rev;
 	int64_t pos, rb = ar->rb, re = ar->re;
+	uint8_t *query;
+
+	query = malloc(l_query);
+	for (i = 0; i < l_query; ++i) // convert to the nt4 encoding
+		query[i] = query_[i] < 5? query_[i] : nst_nt4_table[(int)query_[i]];
 	memset(&a, 0, sizeof(mem_aln_t));
 	a.mapq = mem_approx_mapq_se(opt, ar);
 	bwa_fix_xref(opt->mat, opt->q, opt->r, opt->w, bns, pac, (uint8_t*)query, &qb, &qe, &rb, &re);
@@ -752,6 +761,7 @@ mem_aln_t mem_reg2aln(const mem_opt_t *opt, const bntseq_t *bns, const uint8_t *
 	}
 	a.rid = bns_pos2rid(bns, pos);
 	a.pos = pos - bns->anns[a.rid].offset;
+	free(query);
 	return a;
 }
 
diff --git a/bwamem.h b/bwamem.h
index c2f124c..a856fa5 100644
--- a/bwamem.h
+++ b/bwamem.h
@@ -64,11 +64,11 @@ typedef struct { // TODO: This is an intermediate struct only. Better get rid of
 } bwahit_t;
 
 typedef struct { // This struct is only used for the convenience of API.
-	int rid;
-	int pos;
-	uint32_t is_rev:1, mapq:8, NM:23;
-	int n_cigar;
-	uint32_t *cigar;
+	int rid;         // reference sequence index in bntseq_t
+	int pos;         // forward strand 5'-end mapping position
+	uint32_t is_rev:1, mapq:8, NM:23; // is_rev: whether on the reverse strand; mapq: mapping quality; NM: edit distance
+	int n_cigar;     // number of CIGAR operations
+	uint32_t *cigar; // CIGAR in the BAM encoding: opLen<<4|op; op to integer mapping: MIDSH=>01234
 } mem_aln_t;
 
 #ifdef __cplusplus
@@ -116,13 +116,26 @@ extern "C" {
 	 * @param bns    Information of the reference
 	 * @param pac    2-bit encoded reference
 	 * @param l_seq  length of query sequence
-	 * @param seq    query sequence; conversion ACGTN/acgtn=>01234 to be applied
+	 * @param seq    query sequence
 	 *
 	 * @return       list of aligned regions.
 	 */
-	mem_alnreg_v mem_align1(const mem_opt_t *opt, const bwt_t *bwt, const bntseq_t *bns, const uint8_t *pac, int l_seq, char *seq);
+	mem_alnreg_v mem_align1(const mem_opt_t *opt, const bwt_t *bwt, const bntseq_t *bns, const uint8_t *pac, int l_seq, const char *seq);
 
-	mem_aln_t mem_reg2aln(const mem_opt_t *opt, const bntseq_t *bns, const uint8_t *pac, int l_query, uint8_t *query, const mem_alnreg_t *ar);
+	/**
+	 * Generate CIGAR and forward-strand position from alignment region
+	 *
+	 * @param opt    alignment parameters
+	 * @param bwt    FM-index of the reference sequence
+	 * @param bns    Information of the reference
+	 * @param pac    2-bit encoded reference
+	 * @param l_seq  length of query sequence
+	 * @param seq    query sequence
+	 * @param ar     one alignment region
+	 *
+	 * @return       CIGAR, strand, mapping quality and forward-strand position
+	 */
+	mem_aln_t mem_reg2aln(const mem_opt_t *opt, const bntseq_t *bns, const uint8_t *pac, int l_seq, const char *seq, const mem_alnreg_t *ar);
 
 	/**
 	 * Infer the insert size distribution from interleaved alignment regions
diff --git a/example.c b/example.c
index 6564cbd..b59eec2 100644
--- a/example.c
+++ b/example.c
@@ -32,7 +32,7 @@ int main(int argc, char *argv[])
 		for (i = 0; i < ar.n; ++i) { // traverse each hit
 			mem_aln_t a;
 			if (ar.a[i].secondary >= 0) continue; // skip secondary alignments
-			a = mem_reg2aln(opt, idx->bns, idx->pac, ks->seq.l, (uint8_t*)ks->seq.s, &ar.a[i]); // get forward-strand position and CIGAR
+			a = mem_reg2aln(opt, idx->bns, idx->pac, ks->seq.l, ks->seq.s, &ar.a[i]); // get forward-strand position and CIGAR
 			// print alignment
 			printf("%s\t%c\t%s\t%d\t%d\t", ks->name.s, "+-"[a.is_rev], idx->bns->anns[a.rid].name, a.pos, a.mapq);
 			for (k = 0; k < a.n_cigar; ++k) // print CIGAR
diff --git a/main.c b/main.c
index ba60cf7..fee5bd6 100644
--- a/main.c
+++ b/main.c
@@ -4,7 +4,7 @@
 #include "utils.h"
 
 #ifndef PACKAGE_VERSION
-#define PACKAGE_VERSION "0.7.0-r313"
+#define PACKAGE_VERSION "0.7.0-r314"
 #endif
 
 static int usage()